Common use of Agreements to Sell and Purchase Clause in Contracts

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial Purchasers, and each Initial Purchaser, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, to the Closing Date. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers the Additional Securities, and the Initial Purchasers shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of Additional Securities at the Purchase Price plus accrued interest, if any, to the date of payment and delivery. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), on behalf of the Initial Purchasers, elects to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount of Additional Securities to be purchased by the Initial Purchasers and the date on which such Additional Securities are to be purchased. Such date may be the same as the Closing Date but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm Securities. If any Additional Securities are to be purchased, each Initial Purchaser agrees, severally and not jointly, to purchase the principal amount of Additional Securities (subject to such adjustments to eliminate fractional Securities as you may determine) that bears the same proportion to the total principal amount of Additional Securities to be purchased as the principal amount of Firm Securities set forth in Schedule I opposite the name of such Initial Purchaser bears to the total principal amount of Firm Securities. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraph.

Agreements to Sell and Purchase. The Company (a) Each Selling Stockholder, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriter, and each Initial Purchaserthe Underwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, agrees to purchase from such Selling Stockholder at $93.15 a share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof such Selling Stockholder. (the "Purchase Price"b) plus accrued interest, if any, to the Closing Date. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers the Additional Securities, and the Initial Purchasers shall have a one-time right to purchaseeach Selling Stockholder, severally and not jointly, agrees to sell to the Underwriter the Additional Shares, and the Underwriter shall have the right to purchase up to $30,000,000 principal amount of 487,500 Additional Securities Shares at the Purchase Price plus accrued interest, if any, Price. You may exercise this right in whole or from time to the date of payment and delivery. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), on behalf of the Initial Purchasers, elects to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers you and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 3 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser agrees, severally and not jointly, the Underwriter agrees to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount of Additional Securities to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Selling Stockholder bears to the total principal amount number of Firm Securities. The Company hereby agrees thatShares; provided, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant notwithstanding anything to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of contrary in this paragraph, but without prejudice to the Underwriter’s right to purchase the Additional Shares, the Selling Stockholders shall have the right to generally reallocate sales of any Additional Shares among them such that sales of Additional Shares hereunder may not necessarily be made pro rata among the Selling Stockholders.

Agreements to Sell and Purchase. The Company Each Selling Shareholder, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters the number of Firm ADSs to be sold by such Selling Shareholder set forth in Schedule I hereto opposite the name of such Selling Shareholder, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Selling Shareholder at $12.1444 per ADS (the Company “Purchase Price”) the respective principal amount number of Firm Securities ADSs (subject to such adjustments to eliminate fractional shares as the Managers may determine) that bears the same proportion to the number of Firm ADSs to be sold by such Selling Shareholder as the number of Firm ADSs set forth in Schedule I II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm ADSs. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell each Selling Shareholder, severally and not jointly, hereby grants an option to the Initial Purchasers several Underwriters to purchase up to the number of Additional SecuritiesADSs set forth in Schedule I hereto opposite the name of such Selling Shareholder, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 1,893,801 Additional Securities ADSs at the Purchase Price plus accrued interestPrice, if any, less an amount per ADS equal to any dividends or distributions declared by the date of payment Company and deliverypayable on the Firm ADSs but not payable on the Additional ADSs. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), The Managers may exercise this right on behalf of the Initial Purchasers, elects to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company Underwriters in writing whole or in part but not more than once by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities ADSs to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities ADSs are to be purchased. Such Each purchase date must be at least two business days after the written notice is given (unless the written notice is given prior to the closing date for the Firm ADSs) and may not be the same as the Closing Date but not earlier than the Closing Date nor closing date for the Firm ADSs or later than ten business days after the date of such notice. Additional Securities ADSs may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesADSs. If any On the day, if any, that Additional Securities ADSs are to be purchasedpurchased (the “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities ADSs (subject to such adjustments to eliminate fractional Securities shares as you the Managers may determine) that bears the same proportion to the total principal amount number of Additional Securities ADSs to be purchased on the Option Closing Date as the principal amount number of Firm Securities ADSs set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm Securities. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphADSs.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of _______________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 120 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder or (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphwriting.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 525,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period commencing on the date hereof and ending 90 180 days after the date of the Final Memorandumfinal prospectus relating to the Public Offering (the "Prospectus"), (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock Stock, or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraph.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $[—] a share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees Sellers agree to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of [—] Additional Securities Shares at the Purchase Price plus accrued interestPrice, if anythe Company issuing and selling not more than an additional [—] shares of its Class A Common Stock, and each Selling Stockholder selling not more than the amount set forth opposite such Selling Stockholder’s name in Schedule I hereto; provided, however, that the amount paid by the Underwriters for any Additional Shares shall be reduced by an amount per share equal to any dividends declared by the date of payment Company and deliverypayable on the Firm Shares but not payable on such Additional Shares. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and Deutsche Bank Securities Inc. on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwiseotherwise or (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock. The foregoing restrictions contained in the preceding sentence shall not apply to (Aa) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (Cb) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of which the Underwriters have been advised in writing, (c) the filing by the Company of a registration statement with the Commission on Form S-8 in respect of any shares issued under or the grant of any award pursuant to an employee benefit plan in effect on the date hereof and described in the Final Memorandum, Time of Sale Prospectus or (Dd) the sale or issuance of additional options under or entry into an agreement to sell or issue shares of Class A Common Stock in connection with the Company's existing ’s acquisition of one or more businesses, products or technologies (whether by means of merger, stock option planspurchase, provided asset purchase or otherwise); provided, that such stock options are not exercisable during such 90 day period, or (E) the issuance by aggregate number of shares of Class A Common Stock that the Company of Common Stock may sell or issue or agree to sell or issue pursuant to this clause (d) shall not exceed 10% of the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance total number of shares of the Company's ’s Common Stock issued and outstanding immediately following such 90 the completion of the transactions contemplated by this agreement; and provided further, that each recipient of shares of Class A Common Stock pursuant to this clause (d) shall execute a lock-up agreement substantially in the form of Exhibit A hereto. Notwithstanding the foregoing, if (1) during the last 17 days of the 180-day restricted period the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 180-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 180-day period, the restrictions imposed upon the Company shall continue to a marketingapply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event. The Company shall promptly notify ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and Deutsche Bank Securities Inc. of any earnings release, development news or manufacturing collaborator will not violate event that may give rise to an extension of the terms of this paragraphinitial 180-day restricted period.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $15.28 a purchase price of 97% of the principal amount thereof share (the "“Purchase Price") plus accrued interest, if any, to the Closing Date”). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 1,297,500 Additional Securities Shares at the Purchase Price plus accrued interestPrice, if any, subject to the date of payment and deliveryconditions specified in this paragraph. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters by giving written notice to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company in writing not later than 30 days after the date of this Agreement, which . The exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such purchase date may be the same as the Closing Date (as defined below) but may not be earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On the day, if any, that Additional Securities Shares are to be purchasedpurchased (the “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The option to purchase Additional Shares may be exercised at any time within 30 days after the date of this Agreement, but no more than once. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder or (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphwriting.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of _______________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, or file or cause to be filed a registration statement in respect of, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandumwriting, (DC) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of Common Stock to be used as consideration in connection with future acquisitions, or (D) the grant of options to purchase shares of Common Stock under the Company's Common 1997 Long- Term Incentive Plan or 1997 Non-Employee Directors' Stock following Plan provided such 90 options do not vest prior to the expiration of the 180-day period to a marketingreferenced herein, development or manufacturing collaborator will not violate and provided further, that in the terms case of subclauses (B) and (C) of this paragraph, the recipient of any such shares agrees to execute a lock-up agreement in the form of Exhibit B hereof.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I II hereto opposite its name at a purchase price of 97% of the principal amount thereof $17.523 per share (the "“Purchase Price") plus accrued interest, if any, to the Closing Date”). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount the number of Additional Securities Shares set forth in Schedule I(a) hereto at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which the Prospectus. Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 2(c) hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm Securities. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphShares.

Agreements to Sell and Purchase. The Company and each Selling Shareholder hereby agrees agree, severally and not jointly, to sell to the several Initial PurchasersUnderwriters the Firm Shares in the respective amounts set forth in Schedule I hereto, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company and the Selling Shareholders the respective principal amount numbers of Firm Securities Shares set forth in Schedule I II hereto opposite its name at $____ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to issue and sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 2,250,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date Date, or if after the Closing Date, unless otherwise agreed, such date shall not be earlier than two (2) business days after the date of such notice, nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus (the "Lock-up Period"), (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof that is disclosed in the Prospectus or of and which the Underwriters have been advised in writing, (C) the issuance by the Company of shares of Common Stock or options therefor issued pursuant to stock plans described in the Final MemorandumProspectus, (D) the issuance by the Company of additional shares of Common Stock or options under the Company's existing stock option plansor warrants for shares of Common Stock to suppliers, developers, consultants or other persons in connection with supply, development, consulting, marketing or similar arrangements, provided that the recipient of such stock shares, options are not exercisable during or warrants executes and delivers to you on or before the date of such 90 day period, issuance a "lock-up" agreement substantially in the form provided to the Company by the Underwriters; or (E) the issuance by the Company of shares of Common Stock pursuant to in connection with the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions acquisition by the Company of any businesses, products or technologies. The Company agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇, it will not, during such the period ending 90 day period regarding days after the issuance date of the Prospectus, file or cause to become effective any registration statement relating to any securities of the Company, including a registration statement registering shares under any of the Company's stock plans or other employee benefit plans; provided that the foregoing prohibition shall -------- not apply to any registration statement relating to shares of Common Stock following such 90 day period of the Company to be issued in connection with any acquisition by the Company of any businesses, products or technologies or any registration statement filed in response to the exercise of demand registration rights under the Investor Rights Agreement. Each Selling Shareholder hereby agrees to execute and deliver on or before the Closing Date a marketing, development or manufacturing collaborator will not violate "lock-up" agreement substantially in the terms form of this paragraphExhibit A hereto.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name such Seller at $_______ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, the number of Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the Closing Datenumber of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule II hereto opposite the name of such Underwriter bears to the total number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to issue and sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 1,245,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and which the Underwriters have been advised in writing, or which is described in the Final MemorandumProspectus, (C) the grant of options to purchase Common Stock pursuant to the Company's 1999 Stock Incentive Plan, (D) the issuance by the Company of additional options under shares of Common Stock pursuant to the Company's existing stock option plans1999 Employee Stock Purchase Plan, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of shares of Common Stock pursuant issuable under the Registration Statement on Form S-1, file no. 333-80419 and (F) warrants issued to real estate industry participants in consideration of listings. In addition, each Selling Stockholder agrees that, without the Stock Purchase Agreement between prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Company and American Home Products CorporationUnderwriters, dated as it will not, during the period ending 90 days after the date of December 9the Prospectus, 1999. The Initial Purchasers acknowledge that discussions by initiate any demand for the Company during such 90 day period regarding the issuance registration of any shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphany security convertible into or exercisable or exchangeable for Common Stock.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $27.45 a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 450,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to time in part by giving written notice of each election to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company in writing option not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least two business days after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an "Option Closing Date"), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ Brothers Inc. on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock Shares or any securities convertible into or exercisable or exchangeable for Common Stock Shares or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common StockShares, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock Shares or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock Shares upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and hereof which are described in the Final MemorandumProspectus, (C) the grant of options to purchase Common Shares pursuant to the Company's, the Operating Partnership's and the Service Companies' existing employee, trustee or director benefit plans or (D) the issuance of additional options under Units in connection with the Company's existing stock option plansacquisition of property, provided that such stock options are not exercisable during such 90 day perioddirectly or indirectly, or (E) the issuance by the Company Operating Partnership, notice of Common Stock pursuant which shall be provided to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during Underwriters promptly following any such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphissuance.

Agreements to Sell and Purchase. The Company Each Selling Shareholder, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name such Selling Shareholder at $ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, the number of Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the Closing Datenumber of Firm Shares to be sold by such Selling Shareholder as the number of Firm Shares set forth in Schedule II hereto opposite the name of such Underwriter bears to the total number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees each Selling Shareholder agrees, severally and not jointly, to sell to the Initial Purchasers Underwriters the number of Additional SecuritiesShares set forth in Schedule I hereto opposite the name of such Selling Shareholder, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of Additional Securities Shares at the Purchase Price plus accrued interestPrice. If less than the maximum number of Additional Shares are purchased, if any, each Selling Shareholder will sell the amount which bears the same proportion to the date number of payment and deliveryAdditional Shares purchased by the Underwriters as the number of Additional Shares set forth in Schedule I hereto opposite the name of such Selling Shareholder bears to the total number of Additional Shares. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which ; provided that you shall be limited to three such notices in the aggregate. Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an "Option Closing Date"), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company and each Selling Shareholder hereby agrees agree that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ the Managers on behalf of the Initial PurchasersUnderwriters, it will not, and will not publicly announce any intention to, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or Stock, including Class B Common Stock; (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, including Class B Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise; or (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock. The foregoing sentence restrictions contained in the preceding paragraph shall not apply to (Aa) the sale of the Securities under this AgreementShares to the Underwriters, (B) the issuance of the Underlying Securities upon conversion of the Securities, (Cb) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of which the Managers have been advised in writing; provided that the underlying shares of Common Stock and described Class B Common Stock issued to any Selling Shareholder or other person who has delivered a lock-up agreement pursuant to Section 6(g) hereto shall continue to be subject to the restrictions contained in the Final Memorandumimmediately preceding paragraph or such lock-up agreement, as applicable; (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (Ec) the issuance by the Company of shares of Common Stock and Class B Common Stock or options to purchase shares of Common Stock to, or the repurchase by the Company of unvested shares of Common Stock and Class B Common Stock upon termination of service from, an employee, director, consultant other service provider, pursuant to the Company's stock incentive plans in effect on the date hereof; provided that the shares of Common Stock Purchase Agreement between and Class B Common Stock or options to purchase shares of Common Stock and Class B Common Stock issued to the Company Company's directors and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions executive officers shall be subject to the restrictions contained in the lock-up agreements delivered pursuant to Section 6(h) hereof; (d) the filing by the Company during of any registration statement with the Commission on Form S-8 relating to the offering of securities pursuant to the terms of a stock incentive plan of the Company in effect on the date hereof; (e) transfers by a Selling Shareholder of shares of Common Stock or any security convertible into Common Stock as a bona fide gift or for no consideration and transfers by a Selling Shareholder by will or intestate, provided that in each case, each recipient of such 90 day period regarding shares or convertible securities agrees in writing to be subject to the restrictions described in the immediately preceding paragraph and no filing by any party with the Commission shall be required or shall be voluntarily made in connection with such transfer; (f) transfers by a Selling Shareholder to any trust, partnership or limited liability company for the direct or indirect benefit of such person and/or the immediate family of such Selling Shareholder for estate planning purposes, provided that (i) the trustee of the trust, partnership or the limited liability company, as the case may be, agrees in writing to be subject to the restrictions described in the immediately preceding paragraph, (ii) any such transfer shall not involve a disposition for value, and (iii) no filing by any party with the Commission shall be required or shall be voluntarily made in connection with such transfer; (g) a sale that is required by the restrictions on ownership and transfer set forth in the Company's Amended Certificate of Incorporation; (h) the exercise of outstanding options or warrants by a Selling Shareholder; provided that the underlying shares of Common Stock and Class B Common Stock will be subject to the restrictions described in the immediately preceding paragraph upon exercise or conversion; (i) any transfer by a Selling Shareholder to an affiliate (as that term is defined in Rule 405 under the Securities Act) of such Selling Shareholder, provided that such affiliate agrees in writing to be subject to the restrictions contained in the immediately preceding paragraph and that no filing by any party with the Commission shall be required or shall be voluntarily made in connection with any such transfer, (j) transactions by a Selling Shareholder relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares, provided that no filing by any party with the Commission shall be required or shall be voluntarily made in connection with such open market transactions or (k) the issuance by the Company of shares of Common Stock in connection with acquisitions of other companies up to an amount equal to 19.9% of the Company's fully-diluted Common Stock following (measured as of the Closing Date), provided that each recipient of such 90 shares agrees in writing to be subject to the restrictions described in the immediately preceding paragraph. In addition, each Selling Shareholder, agrees that, without the prior written consent of the Managers on behalf of the Underwriters, it will not, and will not publicly announce the intention to, during the period commencing on the date hereof and ending 180 days after the date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock, including any shares of Class B Common Stock. Each Selling Shareholder also agrees and consents to the entry of stop transfer instructions with the Company's transfer agent and registrar against the transfer of any Shares held by such Selling Shareholder except in compliance with the foregoing restrictions. Notwithstanding the foregoing, if (1) during the last 17 days of the 180-day restricted period the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 180-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 180-day period, the restrictions imposed by this agreement shall continue to a marketingapply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event. The Company shall promptly notify the Managers of any earnings release, development news or manufacturing collaborator will not violate event that may give rise to an extension of the terms of this paragraphinitial 180-day restricted period.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at a price of $ per share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 1,181,250 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may reasonably determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each Seller hereby agrees that, without the prior written consent of M▇▇▇▇▇ S▇▇▇▇▇▇ & Co. Incorporated (“M▇▇▇▇▇ S▇▇▇▇▇▇”) and Credit Suisse Securities (USA) LLC (“Credit Suisse,” and together with M▇▇▇▇▇ S▇▇▇▇▇▇, the “Representatives”) on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwiseotherwise or (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock. The Except as otherwise set forth in separate written agreements with the Underwriters, notwithstanding the previous paragraph, each Selling Stockholder may, but only with respect to up to 25% of the shares of Common Stock currently held by such Selling Stockholder, engage in the transactions described in clauses (1) and (2) of the foregoing sentence paragraph at any time following the 75th day after the date of the Prospectus. Furthermore, the restrictions contained in the preceding paragraph shall not apply to (Aa) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (Cb) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in writing, (c) transactions by a Selling Stockholder relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares, provided that no filing under Section 16(a) of the Exchange Act shall be required or shall be voluntarily made in connection with subsequent sales of Common Stock or other securities acquired in such open market transactions, (d) transfers by a Selling Stockholder of shares of Common Stock or any security convertible into Common Stock as a bona fide gift, (e) distributions by a Selling Stockholder of shares of Common Stock or any security convertible into Common Stock to limited partners or stockholders of the Selling Stockholder; provided that in the Final Memorandumcase of any transfer or distribution pursuant to clause (d) or (e), (Di) each donee or distributee shall enter into a written agreement accepting the restrictions set forth in the preceding paragraph and this paragraph as if it were a Selling Stockholder and (ii) no filing under Section 16(a) of the Exchange Act, reporting a reduction in beneficial ownership of shares of Common Stock, shall be required or shall be voluntarily made in respect of the transfer or distribution during the 75- or 90-day restricted period, (f) the issuance of additional shares of, or options under to purchase shares of, Common Stock, to employees, officers, directors, advisors or consultants of the Company's existing stock option plansCompany pursuant to employee benefit plans disclosed in the Prospectus, provided that prior to the issuance of any such stock shares or options are not exercisable that vest during the 90-day period following the date of the Prospectus, the Company shall cause each recipient of such 90 day periodshares or options to execute and deliver to you a “lock-up” agreement substantially in the form of Exhibit A hereto, (g) the filing of a registration statement on Form S-8, (h) the issuance of securities in connection with the acquisition by the Company or any of its subsidiaries of the securities, businesses, property or other assets of another person or entity or pursuant to any employee benefit plan assumed by the Company in connection with any such acquisition, or (Ei) the issuance by of securities in connection with joint ventures, commercial relationships or other strategic transactions; provided that, in the case of clauses (h) and (i), the aggregate number of shares issued in all such acquisitions and transactions does not exceed 10% of the shares of the Common Stock of the Company outstanding immediately after the offering and prior to any issuance the Company shall cause each recipient of such securities to execute and deliver to you a “lock-up” agreement substantially in the form of Exhibit A hereto. In addition, each Selling Stockholder, agrees that, without the prior written consent of the Representatives on behalf of the Underwriters, it will not, during the period ending 90 days after the date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any shares of Common Stock pursuant or any security convertible into or exercisable or exchangeable for Common Stock. Each Selling Stockholder consents to the Stock Purchase Agreement between entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of any Shares held by such Selling Stockholder except in compliance with the foregoing restrictions. Notwithstanding the foregoing, if (1) during the last 17 days of the 75- or 90-day restricted period the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 75- or 90-day restricted period, the Company announces that it will release earnings results during such the 16-day period beginning on the last day of the 75 day or 90 day restricted period, the restrictions imposed by this agreement shall continue to apply until the expiration of the 18-day period regarding beginning on the issuance of shares the earnings release or the occurrence of the Company's Common Stock following such 90 material news or material event. The Company shall promptly notify the Representatives of any earnings release, news or event that may give rise to an extension of the initial 75- or 90-day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphrestricted period.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $18.70 a share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 2,700,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least two business days after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 6 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ the Representatives on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock (such shares of Common Stock and such Securities, together the “MHG Co. Securities”) or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securitiesMHG Co. Securities, in cash or otherwiseotherwise or (3) file any registration statement with the Commission relating to the offering of any MHG Co. Securities (other than registration statement(s) on Form S-8 to register securities for issuance pursuant to the Company’s 2006 Omnibus Stock Incentive Plan described in the Time of Sale Prospectus). The foregoing sentence restrictions contained in the preceding paragraph shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and which the Underwriters have been advised in writing, (C) the issuance by the Company of MHG Co. Securities under the Company’s 2006 Omnibus Stock Incentive Plan described in the Final MemorandumTime of Sale Prospectus, (D) the issuance by the Company of additional options under shares of Common Stock as part of the Company's existing stock option plansFormation Transactions, provided that such stock options are not exercisable during such 90 day period, or and (E) the issuance by the Company of shares of Common Stock, or by the Operating Company of OC Units, as consideration for one or more acquisitions, provided that (i) the aggregate market value of all such shares of Common Stock, including shares of Common Stock pursuant issuable upon conversion of any such OC Units, does not exceed 10% of the market capitalization of the Company as of 4:30 p.m. (New York City time) on the Closing Date, and (ii) the recipients of any such shares of Common Stock or OC Units shall enter into a written agreement agreeing to the Stock Purchase Agreement between restrictions set forth in the preceding paragraph and this paragraph. Notwithstanding the foregoing, if (1) during the last 17 days of the 180-day restricted period the Company and American Home Products Corporationissues an earnings release; or (2) prior to the expiration of the 180-day restricted period, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company announces that it will release earnings results during such 90 the 16-day period regarding beginning on the last day of the 180-day period, the restrictions imposed by this agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of shares the earnings release. The Company shall promptly notify the Representatives of any earnings release that may give rise to an extension of the Company's Common Stock following such 90 initial 180-day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphrestricted period.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial Purchasers, and each Initial Purchaser, upon Upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, the Selling Stockholder hereby agrees to sell to the several Underwriters, and each Underwriter agrees, severally and not jointly, to purchase from the Company Selling Stockholder at $[ ] per share (the respective principal amount "Purchase Price") the number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, to the Closing Datesuch Underwriter. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company Selling Stockholder agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 525,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such one-time option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company Selling Stockholder in writing at least three business days in advance of the Option Closing Date and not later than 30 days after the date of this Agreement, which notice shall be irrevocable and shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date or three business days after the date such notice is given nor later than ten business days after the date of such noticenotice is given. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase from the principal amount Selling Stockholder, the number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (ia) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for shares of Common Stock or (iib) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (ia) or (iib) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (Ci) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in hereof or with respect to awards under its equity incentive plan outstanding on the Final Memorandumdate hereof, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (Eii) the issuance by the Company of shares of Common Stock or the grant of options or awards to purchase shares of Common Stock pursuant to the Stock Purchase Agreement between employee benefit plans of the Company and American Home Products Corporation, dated in effect as of December 9, 1999. The Initial Purchasers acknowledge that discussions the date hereof or (iii) the issuance by the Company during such 90 day period regarding the issuance of shares of Common Stock (and the filing of a registration statement with respect thereto) in connection with the acquisition by the Company of interests in other companies if the recipients of such shares of Common Stock agree in writing to be bound by the restrictions contained in this paragraph in the same manner as then applied to the Company's . The Selling Stockholder hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, it will not, during the period ending 180 days after the date of the Prospectus, (a) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock following or any securities convertible into or exercisable or exchangeable for shares of Common Stock or (b) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of Common Stock, whether any such 90 day period transaction described in clause (a) or (b) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (i) the Shares to be sold hereunder, (ii) transactions relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares, (iii) any transfer of shares of Common Stock to the Company, (iv) any transfer of shares of Common Stock to any affiliate of the Selling Stockholder (other than the Company), provided that such affiliate agrees in writing to be bound by the restrictions contained in this paragraph in the same manner as then applied to the Selling Stockholder or (v) the sale of shares of Common Stock by the Selling Stockholder to one or more investors in a marketingprivate placement (but not subsequent transfers by such investors to third parties), development or manufacturing collaborator will not violate provided that such investors agree in writing to be bound by the terms of restrictions contained in this paragraphparagraph in the same manner as then applied to the Selling Stockholder.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 435,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-over- allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company and the Parent hereby agrees agree that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it they will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, writing or (EC) the issuance by the Company of Common options under its 1997 Non-Employee Directors' Non-Qualified Stock pursuant to the Option Plan and 1997 Non-Qualified Stock Purchase Agreement between the Company and American Home Products Corporation, dated as Option Plan provided that such options are not exercisable until expiration of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 180 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphperiod.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company at $_______ a share (the respective principal amount "Purchase Price") the number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by the Company as the number of Firm Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees Selling Shareholders agree to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 450,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company Selling Shareholders in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 6 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each Seller hereby agrees that, without the prior written consent of ▇▇▇▇Morg▇▇ ▇▇▇▇n▇▇▇ & ▇o. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, purchase or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) to the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) to the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in writing, (C) to any options granted or shares of Common Stock issued pursuant to existing benefit plans of the Final Memorandum, Company or (D) the issuance with respect to any Selling Shareholder, to any sale of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company shares of Common Stock which are subject to an existing pledge or other security arrangement on the date hereof of which the Underwriters have been advised in writing, in good faith pursuant to the Stock Purchase Agreement between terms of such pledge or arrangement. In addition, each Selling Shareholder, agrees that, without the Company and American Home Products Corporationprior written consent of Morg▇▇ ▇▇▇n▇▇▇ & ▇o. Incorporated on behalf of the Underwriters, dated as it will not, during the period ending 90 days after the date of December 9the Prospectus, 1999. The Initial Purchasers acknowledge that discussions by make any demand for, or exercise any right with respect to, the Company during such 90 day period regarding the issuance registration of any shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphany security convertible into or exercisable or exchangeable for Common Stock.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 1,275,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")the Representatives, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ the Representatives shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you the Representatives may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in writing , (C) the Final Memorandum, grant of options to purchase Common Stock or the issuance of restricted stock to employees or consultants of the Company or (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company any shares of Common Stock pursuant or right to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as acquire shares of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares capital stock of the Company's ; provided that, in the case of clauses (C) and (D), (x) any such option or right to acquire shares of capital stock shall not be exercisable prior to the expiration of the 180 day period (and the Company agrees not to accelerate the exercisability thereof) or the recipient thereof shall have executed a "lock-up" agreement substantially in the form of Exhibit A hereto, (y) any such shares of restricted stock shall have restrictions attached thereto substantially to the effect of the "lock-up" agreement attached as Exhibit A hereto or the recipient thereof shall have executed a "lock-up" agreement substantially in the form of Exhibit A hereto and (z) the recipient of any shares of Common Stock following such 90 day period to shall have executed a marketing, development or manufacturing collaborator will not violate "lock-up" agreement substantially in the terms form of this paragraphExhibit A hereto.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $__.__ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of _________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇Morg▇▇ ▇▇▇▇n▇▇▇ & ▇o. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder; (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and hereof as described in the Final MemorandumRegistration Statement or of which the Underwriters have been advised in writing; (C) the grant of options to purchase Common Stock pursuant to the 1998 Stock Plan and the 1999 Director Option Plan (collectively, the "PLANS"); and (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of shares of Common Stock pursuant to the 1999 Employee Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphPlan.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of _______________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder or (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphwriting.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 600,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 3 hereof solely for the purpose of covering over-over- allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and Banc of America Securities, LLC on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and hereof which is described in the Final Memorandum, (D) Prospectus or of which the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day periodUnderwriters have otherwise been advised in writing, or (EC) the issuance by the Company of shares of Common Stock or options to purchase shares of Common Stock pursuant to the Stock Purchase Agreement between Company's employee benefit plans as in existence on the Company and American Home Products Corporation, dated as date of December 9, 1999this Agreement. The Initial Purchasers acknowledge that discussions by Company hereby represents and warrants that, during the Company during such period ending 90 day period regarding days after the issuance of shares date of the Company's Common Stock following such 90 day period to a marketingProspectus, development or manufacturing collaborator it will not violate release any of its officers, directors or other stockholders; from any lock-up agreements currently existing or hereafter effected without the terms prior written consent of this paragraph▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and Banc of America Securities, LLC.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount number of Firm Securities Shares (to be adjusted by you so as to eliminate fractional shares) as set forth in Schedule I hereto opposite its name at $14.00 a purchase price of 97% of the principal amount thereof share (the "“Purchase Price") plus accrued interest, if any, to the Closing Date”). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company hereby agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 750,000 Additional Securities Shares at the Purchase Price plus accrued interestPrice; provided, if anyhowever, that the amount paid by the Underwriters for any Additional Shares shall be reduced by an amount per share equal to any dividends declared by the date of payment Company and deliverypayable on the Firm Shares but not payable on such Additional Shares. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify time in part by giving written notice to the Company in writing not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. On each day, if any, that Additional Securities may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm Securities. If any Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm Securities. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphShares.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name such Seller at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, the number of Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the Closing Datenumber of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule II hereto opposite the name of such Underwriter bears to the total number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees Selling Stockholders agree to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 491,250 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each Seller hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and hereof that is described in the Final MemorandumProspectus, (C) transactions by any -8- person other than the Company relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares or (D) the issuance grants of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, to purchase up to ______ shares of Class A or (E) the issuance by the Company of Class B Common Stock pursuant to the Stock Purchase Agreement between Company's existing equity based compensation plans, provided that no such option shall be exercisable during the Company and American Home Products Corporationperiod ending 90 days after the date of the Prospectus. In addition, dated as each Selling Stockholder, agrees that, without the prior written consent of December 9▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, 1999. The Initial Purchasers acknowledge that discussions by it will not, during the Company during such period ending 90 day period regarding days after the issuance date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphany security convertible into or exercisable or exchangeable for Common Stock.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $____ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 2,280,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of Morgan Stanley & Co. Incorporated on behalf of the Underwriters, it will ▇▇▇, d▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the he period ending 90 days after the date of the Final Memorandum, Prospectus: (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock Stock; or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option outstanding under the Company's existing stock option plan or the issuance of new options thereunder or any warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in writing prior to the Final Memorandumdate hereof, or (DC) the issuance and sale to AIG of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company shares of Common Stock pursuant to the Stock exercise by AIG of the AIG Option and the Purchase Agreement between the Company and American Home Products CorporationAIG dated November 19, dated 2001 (the "PURCHASE AGREEMENT"), as such agreements are more fully described in the Prospectus under the caption "Certain Relationships And Related Transactions -- AIG Option and Concurrent Purchase of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphShares."

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $22.1178 a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional Securities, Shares and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, on a pro-rata basis from the Company up to $30,000,000 principal amount of 516,684 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of Morgan Stanley & Co. Incorporated on behalf of the Underwriters, it wi▇▇ ▇▇▇, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock Stock, provided that the Company may grant options under the Company's existing plans to employees who are not officers or directors of the Company, or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, writing or (EC) the issuance transactions by any person other than the Company in shares of Common Stock pursuant to or other securities that in either case were acquired in open market transactions after the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares completion of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate offering of the terms of this paragraphShares.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 2,250,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter 8 into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and which the Underwriters have been advised in writing, (C) the issuance of Common Stock or the grant of an option to purchase Common Stock under our stock plans described in the Final MemorandumProspectus, (D) the issuance of additional options under Common Stock in connection with the Company's existing stock option plansacquisition of another company if recipients of the Common Stock agree to be bound for 180 days by the restrictions contained in this paragraph, provided that such stock options are not exercisable during such 90 day periodand the filing of a registration statement with respect thereto, or (E) the issuance transactions by the Company any person other than us, relating to shares of Common Stock pursuant to or other securities acquired in open market or other transactions after the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms completion of this paragraphoffering.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial Purchasers, and each Initial Purchaser, upon Upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, the Selling Stockholder hereby agrees to sell to the several Underwriters, and each Underwriter agrees, severally and not jointly, to purchase from the Company Selling Stockholder at $34.02 per share (the respective principal amount "Purchase Price") the number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, to the Closing Datesuch Underwriter. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company Selling Stockholder agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 638,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such one-time option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company Selling Stockholder in writing at least three business days in advance of the Option Closing Date and not later than 30 days after the date of this Agreement, which notice shall be irrevocable and shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date or three business days after the date such notice is given nor later than ten business days after the date of such noticenotice is given. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase from the principal amount Selling Stockholder, the number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (ia) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for shares of Common Stock or (iib) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (ia) or (iib) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (Ci) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in hereof or with respect to awards under its equity incentive plan outstanding on the Final Memorandumdate hereof, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (Eii) the issuance by the Company of shares of Common Stock or the grant of options or awards to purchase shares of Common Stock pursuant to the Stock Purchase Agreement between employee benefit plans of the Company and American Home Products Corporation, dated in effect as of December 9, 1999. The Initial Purchasers acknowledge that discussions the date hereof or (iii) the issuance by the Company during such 90 day period regarding the issuance of shares of Common Stock (and the filing of a registration statement with respect thereto) in connection with the acquisition by the Company of interests in other companies if the recipients of such shares of Common Stock agree in writing to be bound by the restrictions contained in this paragraph in the same manner as then applied to the Company's . The Selling Stockholder hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, it will not, during the period ending 180 days after the date of the Prospectus, (a) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock following or any securities convertible into or exercisable or exchangeable for shares of Common Stock or (b) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of Common Stock, whether any such 90 day period transaction described in clause (a) or (b) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (i) the Shares to be sold hereunder, (ii) transactions relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares, (iii) any transfer of shares of Common Stock to the Company, (iv) any transfer of shares of Common Stock to any affiliate of the Selling Stockholder (other than the Company), provided that such affiliate agrees in writing to be bound by the restrictions contained in this paragraph in the same manner as then applied to the Selling Stockholder or (v) the sale of shares of Common Stock by the Selling Stockholder to one or more investors in a marketingprivate placement (but not subsequent transfers by such investors to third parties), development or manufacturing collaborator will not violate provided that such investors agree in writing to be bound by the terms of restrictions contained in this paragraphparagraph in the same manner as then applied to the Selling Stockholder.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name such Seller at $_____ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, the number of Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the Closing Datenumber of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule II hereto opposite the name of such Underwriter bears to the total number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 903,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-over- allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each Seller hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending at least 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in writing, (C) transactions by any person other than the Final MemorandumCompany relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares, (D) the grant of options to purchase Common Stock or the issuance of additional options under restricted stock pursuant to the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period1998 Stock Plan, or (E) the issuance by the Company of purchase rights and shares of Common Stock pursuant to the Company's 1999 Employee Stock Purchase Agreement between Plan. In addition, each Selling Shareholder, agrees that, without the Company and American Home Products Corporationprior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, dated as it will not, during the period ending at least 90 days after the date of December 9the Prospectus, 1999. The Initial Purchasers acknowledge that discussions by make any demand for, or exercise any right with respect to, the Company during such 90 day period regarding the issuance registration of any shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphany security convertible into or exercisable or exchangeable for Common Stock.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $______ a share (the Company "PURCHASE PRICE") the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees Selling Shareholders agree to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of _______________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company Selling Shareholders in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each Seller hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, writing or (EC) the issuance transactions by any person other than the Company relating to shares of Common Stock pursuant to or other securities acquired in open market transactions after the Stock Purchase Agreement between completion of the Company and American Home Products Corporationoffering of the Shares. In addition, dated as each Selling Shareholder, agrees that, without the prior written consent of December 9▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, 1999. The Initial Purchasers acknowledge that discussions by it will not, during the Company during such 90 day period regarding ending 180 days after the issuance date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphany security convertible into or exercisable or exchangeable for Common Stock.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial Purchasers, and each Initial Purchaser, upon On the basis of the representations and warranties herein containedcontained in this Agreement, but and subject to its terms and conditions, the conditions hereinafter statedFund agrees to issue and sell, and each Underwriter agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name Fund at a purchase price per Share of 97% of the principal amount thereof $10.00 (the "Purchase Price") plus accrued interest, if any, to the Closing Datenumber of Firm Shares set forth opposite the name of such Underwriter in Schedule I hereto. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company Fund further agrees to issue and sell to the Initial Purchasers the Additional Securities, Shares and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 6,000,000 Additional Securities Shares from the Fund at the Purchase Price plus accrued interest, if any, to the date of payment and delivery. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), on behalf of the Initial Purchasers, elects to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount of Additional Securities to be purchased by the Initial Purchasers and the date on which such Additional Securities are to be purchased. Such date may be the same as the Closing Date but not earlier than the Closing Date nor later than ten business days after the date of such noticePrice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. The Underwriters may exercise their right to purchase Additional Shares in whole or in part from time to time by giving written notice thereof to the Fund within 60 days after the date of this Agreement. You shall give any such notice on behalf of the Underwriters and such notice shall specify the aggregate number of Additional Shares to be purchased pursuant to such exercise and the date for payment and delivery thereof, which date shall be a business day (i) no earlier than two business days after such notice has been given (and, in any event, no earlier than the Closing Date (as hereinafter defined)) and (ii) no later than ten business days after such notice has been given. If any Additional Securities Shares are to be purchased, each Initial Purchaser agreesUnderwriter, severally and not jointly, agrees to purchase from the principal amount Fund the number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that which bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased from the Fund as the principal amount number of Firm Securities Shares set forth in Schedule I opposite the name of such Initial Purchaser Underwriter in Schedule I bears to the total principal amount number of Firm SecuritiesShares. The Company hereby For each of the Shares sold to the several Underwriters pursuant to this Agreement, the Investment Manger (not the Fund) agrees thatto pay or cause to be paid to ▇▇▇▇▇▇▇▇▇, without the prior written consent of ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇▇ on behalf Securities Corporation for its own account and the account of each Underwriter a fee equal to an amount computed by multiplying (A) $0.50, by (B) the sum of the Initial Purchasersnumber of Shares purchased by ▇▇▇▇▇▇▇▇▇, it will not, during ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇▇ Securities Corporation and each such Underwriter on the period ending 90 days after the date of the Final Memorandum, Closing Date and any Option Closing Date (as defined below in Section 4). The Fund hereby agrees not to (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock Shares or any securities convertible into or exercisable or exchangeable for Common Stock Shares or (ii) enter into any swap or other arrangement that transfers to another, in whole all or in part, any a portion of the economic consequences of associated with the ownership of the any Common Stock, Shares (regardless of whether any such transaction of the transactions described in clause (i) or (ii) above is to be settled by the delivery of Common Stock Shares, or such other securities, in cash or otherwise. The foregoing sentence shall not apply ), except to the Underwriters pursuant to this Agreement or as described in the Prospectus, including the Fund's Automatic Divided Reinvestment Plan (A) the sale "Plan"), for a period of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on 180 days after the date of and described in the Final MemorandumUnderwriting Agreement without the prior written consent of ▇▇▇▇▇▇▇▇▇, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇▇ Securities Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraph.

Agreements to Sell and Purchase. The Company hereby agrees to issue and sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company at $[ ] per share (the "Purchase Price") the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, to the Closing Datesuch Underwriter. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of [ ] Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 [ ] days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares hereunder or (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphwriting.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $[.] a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of [.] Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-over- allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder; (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock as described in the Prospectus or upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of which the Underwriters have been advised in writing; (C) the issuance of purchase rights, shares of Common Stock or the grant of options to purchase Common Stock pursuant to the 2000 Stock Plan, the 2000 Director Option Plan or the 2000 Employee Stock Purchase Plan; and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) Series G Preferred Stock to The ▇▇▇▇ Disney Corporation and the issuance by the Company of Common Series H Preferred Stock pursuant to the Stock Purchase Agreement between the Company and American At Home Products Corporation, dated each as of December 9, 1999. The Initial Purchasers acknowledge that discussions by described in the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphProspectus.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 705,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-over- allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap swap, hedging or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder or (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described hereof as disclosed in the Final Memorandum, Prospectus or (DC) the issuance grant of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such the period ending 90 day period, or (E) days after the issuance by date of the Company of Common Stock Prospectus pursuant to option plans existing on the Stock Purchase Agreement between date hereof, as any such plan may be amended after the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphdate hereof.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $[—] a share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers the Additional SecuritiesUnderwriters, and the Initial Purchasers Underwriters shall have a one-time the right to purchasepurchase from the Company, severally and not jointly, up to $30,000,000 principal amount of the Additional Securities Shares at the Purchase Price plus accrued interestPrice; provided, if anyhowever, that the amount paid by the Underwriters for any Additional Shares shall be reduced by an amount per share equal to any dividends declared by the date of payment Company and deliverypayable on the Firm Shares but not payable on such Additional Shares. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and ▇.▇. ▇▇▇▇▇▇ Securities Inc. on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwiseotherwise or (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock. The foregoing sentence restrictions contained in the preceding paragraph shall not apply to (Aa) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (Cb) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, hereof provided that such stock options are not exercisable during such 90 day periodoption, warrant or security is identified in the Time of Sale Prospectus, (Ec) the issuance by the Company of Common Stock or other securities convertible into or exercisable for shares of Common Stock pursuant to the Company Stock Purchase Agreement between Plans provided that such Company Stock Plans are described in the Company and American Home Products CorporationTime of Sale Prospectus, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions (d) the entry into an agreement providing for the issuance by the Company during of shares of Common Stock or any security convertible into or exercisable for shares of Common Stock in connection with the acquisition by the Company or any of its subsidiaries of the securities, business, property or other assets of another person or entity or pursuant to an employee benefit plan assumed by the Company in connection with such 90 day period regarding acquisition, and the issuance of any such securities pursuant to any such agreement, or (e) the entry into an agreement providing for the issuance of shares of the Company's Common Stock following or any security convertible into or exercisable for shares of Common Stock in connection with joint ventures, commercial relationships or other strategic transactions, and the issuance of any such 90 securities pursuant to any such agreement; provided that in the case of clauses (d) and (e), (i) the number of shares of Common Stock issued or issuable pursuant to such clauses (d) and (e) shall not, in the aggregate, exceed 20% of the Shares actually sold pursuant to this Agreement and (ii) upon receipt of such securities, each recipient of such securities issued pursuant thereto shall be subject to the transfer restrictions contained in the lockup agreement attached as Exhibit A hereto with respect to such issued securities and the Company shall enter stop transfer instructions on such securities in accordance with Section 1(gg). Notwithstanding the foregoing, if (1) during the last 17 days of the 180-day restricted period the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 180-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 180-day period, the restrictions imposed by this agreement shall continue to a marketingapply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event. The Company shall promptly notify ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and ▇.▇. ▇▇▇▇▇▇ Securities Inc. of any earnings release, development news or manufacturing collaborator will not violate event that may give rise to an extension of the terms of this paragraphinitial 180-day restricted period.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name such Seller at $_______ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, the number of Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the Closing Datenumber of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule II hereto opposite the name of such Underwriter bears to the total number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to issue and sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 360,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each Seller hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of any Shares to the Securities under this AgreementUnderwriters to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option stock options or warrant or the conversion of a security warrants outstanding on the date of and hereof or described as outstanding or reserved for issuance under the option plans described in the Final MemorandumProspectus, (D) the issuance or any other issuances of additional Common Stock or options to acquire Common Stock hereafter under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day periodor equity incentive plans described in the Prospectus, or (EC) the issuance by the Company of Common Stock pursuant to under the Stock Purchase Agreement between employee stock purchase plan described in the Company and American Home Products CorporationProspectus. In addition, dated as each Selling Stockholder agrees that, without the prior written consent of December 9▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, 1999. The Initial Purchasers acknowledge that discussions by it will not, during the Company during such period ending 90 day period regarding days after the issuance date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphany security convertible into or exercisable or exchangeable for Common Stock.

Agreements to Sell and Purchase. (a) The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $26.25 a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE"). (b) plus accrued interest, if any, to the Closing Date. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 1,048,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm Securities. Shares. (c) The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ Managers on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 60 days after the date of the Final Memorandum, Prospectus: (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock Stock; or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwiseotherwise or (iii) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exerciseable for Common Stock. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares hereunder, or (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option outstanding under the Company's existing stock option plan , the vesting of any restricted stock unit outstanding under the Company's existing stock incentive plan or the issuance of new options or restricted stock units thereunder or any warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in writing prior to the Final Memorandum, date hereof or (DC) the issuance concurrent sale of 3,341,000 common shares (plus up to an additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant 334,000 common shares to the Stock Purchase Agreement between extent the Company and over allotment option is exercised) to American Home Products CorporationInternational Group, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraph.Inc.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of _______________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇Morg▇▇ ▇▇▇▇n▇▇▇ & ▇o. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described hereof that is disclosed in the Final Memorandum, (D) the issuance Prospectus or of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraph.which the

Agreements to Sell and Purchase. The Company Each Selling Stockholder hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Selling Stockholder at $32.98 a share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Selling Stockholder as the number of Firm Shares set forth in Schedule I II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company St. ▇▇▇▇ Travelers agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 3,930,916 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Each of the Company and each Selling Stockholder hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and ▇▇▇▇▇▇▇ Lynch, Pierce, ▇▇▇▇▇▇ & ▇▇▇▇▇ Incorporated, on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock Stock; or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise; or (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock. The foregoing sentence restrictions contained in the preceding paragraph shall not apply to (Aa) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (Cb) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandumwriting, (Dc) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance grant by the Company of Common Stock stock options, restricted stock or other awards pursuant to the Stock Purchase Agreement between Company’s benefit plans in existence on the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions date hereof or proposed to be approved by the Company Company’s stockholders at their 2005 annual meeting; provided that such options, restricted stock or awards do not become exercisable or vest during such 90 90-day period regarding period, (d) the issuance sale of shares by St. ▇▇▇▇ Travelers in connection with the Forward Agreements, (e) the sale of shares by St. ▇▇▇▇ Travelers underlying the Mandatory Exchangeables, (f) the sale of shares of Common Stock by St. ▇▇▇▇ Travelers pursuant to the Repurchase Agreement or (g) transactions by each Selling Stockholder relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares, provided that for the purposes of this clause (g) no filing under Section 16(a) of the Securities Exchange Act, shall be required or shall be voluntarily made in connection with subsequent sales of Common Stock or other securities acquired in such open market transactions. In addition, the Selling Stockholders agree that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and ▇▇▇▇▇▇▇ Lynch, Pierce, ▇▇▇▇▇▇ & ▇▇▇▇▇ Incorporated, on behalf of the Underwriters, they will not, during the period ending 90 days after the date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock. The Selling Stockholders consent to the entry of stop transfer instructions with the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate ’s transfer agent and registrar against the terms transfer of this paragraphany Shares held by the Selling Stockholders except in compliance with the foregoing restrictions.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $___a share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 865,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇M▇▇▇▇▇ ▇S▇▇▇▇▇▇ on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwiseotherwise or (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, except for registration statements on Form S-8 (or equivalent forms). The foregoing sentence restrictions contained in the preceding paragraph shall not apply to (Aa) the sale of the Securities under this AgreementShares to be sold hereunder, (Bb) the issuance by the Company of restricted shares of Common Stock or options to acquire Common Stock pursuant to the Underlying Securities upon conversion of Company’s employee benefit plans, stock option plans or other employee compensation plans described in the SecuritiesProspectus, (Cc) the issuance by the Company of shares of Common Stock upon the exercise of an option that was issued pursuant to the Company’s employee benefit plans, stock option plans or other employee compensation plans described in the Prospectus, (d) the issuance by the Company of shares of Common Stock upon exercise of a warrant or the conversion of a security outstanding on the date of and described hereof that has been disclosed in the Final Memorandum, (D) Prospectus or of which the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day periodUnderwriters have been advised in writing, or (Ee) the issuance by the Company of up to an aggregate of three hundred thousand (300,000) shares of Common Stock pursuant (or securities convertible into or exercisable or exchangeable for Common Stock) in connection with acquisitions or other business combinations, strategic alliances or similar relationships, including, without limitation, relationships with original equipment manufacturers, distributors, resellers and suppliers; provided that such recipient shall sign and deliver a lock-up agreement in the form attached hereto as Exhibit A. Notwithstanding the foregoing, if (1) during the last 17 days of the 180-day restricted period the Company issues an earnings release or material news or a material event relating to the Stock Purchase Agreement between Company occurs; or (2) prior to the expiration of the 180-day restricted period, the Company and American Home Products Corporationannounces that it will release earnings results during the 16-day period beginning on the last day of the 180-day period, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions the restrictions imposed by the Company during such 90 preceding paragraph shall continue to apply until the expiration of the 18-day period regarding beginning on the issuance of shares the earnings release or the occurrence of the Company's Common Stock following such 90 material news or material event. The Company shall promptly notify M▇▇▇▇▇ S▇▇▇▇▇▇ of any earnings release, news or event that may give rise to an extension of the initial 180-day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphrestricted period.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount number of Firm Securities Shares set forth opposite the name of such Underwriter in Schedule I hereto opposite its name at a purchase price of 97% of the principal amount thereof US$8.50 per Ordinary Share (the "“Purchase Price") plus accrued interest, if any, to the Closing Date”). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company hereby agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 585,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), The Representatives may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least two business days after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you the Representatives may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm Securities. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphShares.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite its name at $____ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of [________] Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder (B) the issuance grant of options pursuant to the Underlying Securities upon conversion of 1998 Incentive Plan or the Securities, 1998 Directors Plan (C) the sale of stock pursuant to the 1998 Purchase Plan (D) the grant of any option or warrant pursuant to an equipment lease or accounts receivable finance transaction (E) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, writing or (DF) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance sale by the Company of Common Stock pursuant securities for an aggregate consideration not to exceed $__________, in connection with an investment by one or more strategic partners, provided that the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as holders of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period securities are subject to a marketing, development or manufacturing collaborator will not violate lock-up for six (6) months following the sale with substantially the same terms of this paragraphas set forth in the Lock-Up Agreements (as defined in Section 5(h) herein).

Agreements to Sell and Purchase. The Company Selling Shareholder, hereby agrees to sell to the several Initial PurchasersUnderwriter, and each Initial Purchaserthe Underwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, agrees to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name Selling Shareholder at $23.74125 a purchase price of 97% of the principal amount thereof share (the "“Purchase Price"”) plus accrued interest, if any, the Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine) to be sold by the Closing DateSelling Shareholder hereunder. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company Selling Shareholder, agrees to sell to the Initial Purchasers Underwriter the Additional SecuritiesShares, and the Initial Purchasers Underwriter shall have a one-time the right to purchase, severally and not jointly, purchase the Additional Shares (which in the aggregate shall be up to $30,000,000 principal amount of 361,315 Additional Securities Shares) at the Purchase Price plus accrued interestPrice, if anyprovided, however, that the amount paid by the Underwriter for any Additional Shares shall be reduced by an amount per share equal to the date of payment and delivery. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), on behalf of the Initial Purchasers, elects to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify any dividends declared by the Company and payable on the Firm Shares but not payable on such Additional Shares. You may exercise this right in writing whole or from time to time in part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriter and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser agrees, severally and not jointly, the Underwriter agrees to purchase the principal amount number of the total number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount of Additional Securities to be purchased as on such Option Closing Date. Each of the principal amount of Firm Securities set forth in Schedule I opposite Company and the name of such Initial Purchaser bears to the total principal amount of Firm Securities. The Company Selling Shareholder, severally and not jointly, hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers& Co. LLC, it will not, during the period commencing on the date hereof and ending 90 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock beneficially owned (as such term is used in Rule 13d-3 of the Exchange Act) or any other securities so owned convertible into or exercisable or exchangeable for Common Stock Stock; or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise; or (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock. The foregoing sentence restrictions contained in the preceding paragraph shall not apply to (Aa) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (Cb) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof or the issuance or grant by the Company of options, shares, restricted stock units, restricted stock or other equity or equity-linked securities under any employee benefit plan existing on the date hereof, (c) transactions by the Selling Shareholder relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares, provided that no filing under Section 16(a) of the Exchange Act shall be required or shall be voluntarily made in connection with subsequent sales of Common Stock or other securities acquired in such open market transactions, (d) transfers by the Selling Shareholder of shares of Common Stock or any security convertible into Common Stock as a bona fide gift, (e) distributions by the Selling Shareholder of shares of Common Stock or any security convertible into Common Stock to limited partners or stockholders of the Selling Shareholder, (f) transfers of Common Stock by the Selling Shareholder (1) in connection with the sale or other bona fide transfer in a single transaction of all or substantially all of the Selling Shareholder’s capital stock, partnership interests, membership interests or other similar equity interests, as the case may be, or all or substantially all of the Selling Shareholder’s assets, in any such case not undertaken for the purpose of avoiding the restrictions imposed by this Agreement or (2) to another corporation, partnership, limited liability company or other business entity so long as the transferee is an affiliate (as defined in Rule 405 under the Securities Act) of the Selling Shareholder and described such transfer is not for value; provided that in the Final Memorandumcase of any transfer or distribution pursuant to clause (d), (De), or (f), (i) each donee, distributee or transferee shall enter into a written agreement accepting the restrictions set forth in the preceding paragraph and this paragraph as if it were the Selling Shareholder and (ii) no filing under Section 16(a) of the Exchange Act, reporting a reduction in beneficial ownership of shares of Common Stock, shall be required or shall be voluntarily made in respect of the transfer or distribution during the 90-day restricted period, or (g) the issuance establishment of additional options a trading plan pursuant to Rule 10b5-1 under the Company's existing stock option plansExchange Act for the transfer of shares of Common Stock, provided that such stock options are plan does not exercisable during such 90 day period, or (E) provide for the issuance by the Company transfer of Common Stock pursuant during the 90-day restricted period and no public announcement or filing under the Exchange Act regarding the establishment of such plan shall be required of or voluntarily made by or on behalf of the Selling Shareholder or the Company. In addition, the Selling Shareholder, agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. LLC, it will not, during the period ending 90 days after the date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock. The Selling Shareholder consents to the Stock Purchase Agreement between entry of stop transfer instructions with the Company Company’s transfer agent and American Home Products Corporation, dated as registrar against the transfer of December 9, 1999. The Initial Purchasers acknowledge that discussions any Shares held by the Company during such 90 day period regarding Selling Shareholder except in compliance with the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphforegoing restrictions.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company at $______ a share (the "PURCHASE PRICE") the respective principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, to the Closing Datesuch Underwriter. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to issue and sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 525,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-over- allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, writing or (DC) the issuance grant or exercise of additional options to purchase Common Stock under the Company's existing stock option employee benefit plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraph.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company at $_____ a share (the respective principal amount "Purchase Price") the number of Firm Securities Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, to the Closing Datesuch Underwriter. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 300,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇Morg▇▇ ▇▇▇▇n▇▇▇ & ▇o. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, lend, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraph.of

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $o a share (the Company "PURCHASE PRICE") the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of o Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each Seller hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and Credit Suisse First Boston Corporation on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock Shares or any securities convertible into or exercisable or exchangeable for Common Stock Shares or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common StockShares, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock Shares or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock Shares upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and which the Underwriters have been advised in writing, (C) issuances of stock options, restricted stock or other awards granted pursuant to the Company's employee equity incentive plan or non-employee directors' equity incentive plan as described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, Prospectus; provided that such stock options are awards do not become exercisable or vest during such 90 90-day period, or (ED) the issuance issuances by the Company of Common Stock Shares in connection with the merger or amalgamation with, or acquisition of another corporation or entity or the acquisition of the assets or properties of any such corporation or entity and the related entry into a merger, amalgamation or acquisition agreement with respect to such merger, amalgamation or acquisition, so long as each of the recipients of the Common Shares agrees in writing prior to the consummation of any such transaction, pursuant to an instrument in form and substance reasonably satisfactory to ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and Credit Suisse First Boston Corporation, to be bound by the Stock Purchase Agreement between provisions of this paragraph for the remainder of such 90-day period as if such recipients were the Company, and the public announcements and related filings of registration statements with respect to any such issuances; provided that if the Company and American Home Products Corporationis unable to obtain signed, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by written lock-up agreements from the Company during such 90 day period regarding the issuance of shares recipients of the Company's Common Stock following such 90 day period to Shares in connection with a marketingmerger, development amalgamation or manufacturing collaborator will not violate the terms acquisition as described in clause (D) of this paragraph, then only the entry into the merger, amalgamation or acquisition agreement, the public announcement of such transaction and the related filing of a registration statement shall be permitted and not the related issuance of the Common Shares. In addition, each Selling Shareholder, agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated and Credit Suisse First Boston Corporation on behalf of the Underwriters, it will not, during the period ending 90 days after the date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any Common Shares or any security convertible into or exercisable or exchangeable for Common Shares.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial Purchasers, and each Initial PurchaserEach Selling Shareholder, upon the basis of the representations and warranties herein contained, but subject to the terms and conditions hereinafter stated, hereby agrees, severally and not jointly, to sell to the several Underwriters, and each Underwriter, upon the basis of the representations and warranties herein contained, but subject to the terms and conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Selling Shareholder at $14.40 a share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Shares to be sold by such Selling Shareholder as the number of Shares set forth in Schedule I II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, each Selling Shareholder, hereby agrees, severally and not jointly, as and to the Company agrees extent indicated in Schedule I hereto, to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount an aggregate of 1,500,000 Additional Securities Shares at the Purchase Price plus accrued interestPrice, if anyprovided, however, that the amount paid by the Underwriters for any Additional Shares shall be reduced by an amount per share equal to any dividends declared by the date of payment Company and deliverypayable on the Firm Shares but not payable on such Additional Shares. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), The Representatives may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date nor closing date for the Firm Shares or later than ten business days after the date of such notice. On each day, if any, that Additional Securities may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm Securities. If any Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you the Representatives may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm Securities. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphShares.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $21.4975 a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 450,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date or the Option Closing Date, as the case may, (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of Shares to be sold hereunder or under the Securities under this Company's Dividend Reinvestment Plan, its Stock Option and Incentive Plan, or the ▇▇▇▇▇▇▇▇ ▇▇▇▇ Agreement, (B) the issuance of the Underlying Securities or upon conversion of the SecuritiesSeries A Cumulative Convertible Preferred Stock, (C) the issuance by the Company of shares of Common Series B Cumulative Convertible Preferred Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphSeries C Cumulative Convertible Preferred Stock.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name names at U.S.$_____ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of __________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder or (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphwriting.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name such Seller at a purchase price of 97% of the principal amount thereof $ per share (the "Purchase Price") plus accrued interest, if any, the number of Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the Closing Datenumber of Firm Shares to be sold by such Seller as the respective number of Firm Shares set forth in Schedule II hereto opposite the name of such Underwriter bears to the total number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of 2,175,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to time in part by giving written notice of each election to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company in writing option not later than 30 days after the date of this Agreement, which . Any such exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least one business day after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date (as defined below) nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities are to be purchasedOn each Option Closing Date (as defined below), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each of the Sellers (other than the Sponsors (as defined below) who have delivered "lock-up" agreements substantially in the form of Exhibit A hereto), severally and not jointly, hereby agrees that, without the prior written consent of ▇▇▇▇▇▇▇ Lynch, Pierce, ▇▇▇▇▇▇ & ▇▇▇▇▇ Incorporated and ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated, on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock Shares or any securities convertible into or exercisable or exchangeable for Common Stock Shares or (ii) file any registration statement with the Commission relating to the offering of any Common Shares or any securities convertible into or exercisable or exchangeable for Common Shares or (iii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common StockShares, whether any such transaction described in clause (i), (ii) or (iiiii) above is to be settled by delivery of Common Stock Shares or such other securities, in cash or otherwise. The foregoing sentence restrictions contained in the preceding paragraph shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock Shares upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in writing or (C) transactions by any person other than the Company relating to Common Shares or other securities acquired in open market transactions after the completion of the offering of the Shares. In addition, each Selling Shareholder, (other than the Sponsors who have delivered "lock-up" agreements substantially in the Final Memorandumform of Exhibit A hereto), severally and not jointly, agrees that, without the prior written consent of ▇▇▇▇▇▇▇ Lynch, Pierce, ▇▇▇▇▇▇ & ▇▇▇▇▇ Incorporated and ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co., Incorporated, on behalf of the Underwriters, it will not, during the period ending 180 days after the date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any Common Shares or any security convertible into an exercisable or exchangeable for Common Shares. The undersigned also agrees and consents to the entry of stop transfer instructions with the Company's transfer agent and registrar against the transfer of the undersigned's Common Shares except in compliance with the foregoing restrictions. Notwithstanding the foregoing, if (D1) during the last 17 days of the 180-day restricted period the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 180-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 180-day period, the restrictions imposed by this letter shall continue to apply until the expiration of the 18-day period beginning on the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, earnings release or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares occurrence of the Company's Common Stock following such 90 day period to a marketing, development material news or manufacturing collaborator will not violate the terms of this paragraphmaterial event.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $________ a share (the Company "PURCHASE PRICE") the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees Selling Stockholders, severally and not jointly, agree to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 480,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company Custodian in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees agrees, on its own behalf and on behalf of each stockholder of the Company listed on Schedule III hereto (the "SUBJECT STOCKHOLDERS"), that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not and each Subject Stockholder will not, during the period commencing on the date hereof and ending 90 days after the date of the Final Memorandumfinal prospectus relating to the Public Offering (as defined herein), (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock Stock, or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of which the Underwriters have been advised in writing or (C) transactions by any person other than the Company relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares. In addition, the Company, on behalf of each Subject Stockholder, agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, each Subject Stockholder will not, during the period ending 90 days after the date of the Prospectus, make any demand for, or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock. The Company agrees to give notice to each Subject Stockholder bound by the foregoing "lock-up" agreement pursuant to Section 4(c) of Exhibit D to that certain Stockholders Agreement, dated as of August 2, 1994, as amended, among the Aftermarket Technology Holdings Corp. (which was subsequently merged with and described in into the Final MemorandumCompany) and certain of its stockholders, optionholders and warrantholders (the "STOCKHOLDERS AGREEMENT.") The Representatives hereby agree that those stockholders of the Company listed on Schedule IV attached hereto are not bound by the foregoing "lock-up" agreement notwithstanding that such stockholders are also parties to the Stockholders Agreement. Each Selling Stockholder hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, it will not, during the period commencing on the date hereof and ending 90 days after the date of the final prospectus relating to the Public Offering, (D1) the issuance offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of additional options under the Company's existing stock option plans, provided that such stock options are not Common Stock or any securities convertible into or exercisable during such 90 day periodor exchangeable for Common Stock, or (E2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the Shares to be sold hereunder, (B) the issuance by the Company of shares of Common Stock pursuant to upon the Stock Purchase Agreement between exercise of an option or warrant or the conversion of a security outstanding on the date hereof of which the Underwriters have been advised in writing or (C) transactions by any person other than the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of relating to shares of the Company's Common Stock following such or other securities acquired in open market transactions after the completion of the offering of the Shares. In addition, each Selling Stockholder, agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, it will not, during the period ending 90 day period to a marketingdays after the date of the Prospectus, development make any demand for, or manufacturing collaborator will not violate exercise any right with respect to, the terms registration of this paragraphany shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name names at U.S.$38.95 a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 720,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date or the fourth business day after the date of such notice, nor later than ten the tenth business days day after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day periodwriting, or (EC) the issuance by the Company grant of options to purchase Common Stock pursuant to the Stock Purchase Agreement between Company's equity-based compensation plans described in the Prospectus, provided that such options are not exercisable within such 90 day period. Notwithstanding the foregoing, the Company and American Home Products Corporationmay issue shares of Common Stock, dated or any securities convertible into or exercisable or exchangeable for Common Stock, as full or partial consideration in connection with any future acquisitions of December 9, 1999. The Initial Purchasers acknowledge that discussions companies or businesses by the Company during such 90 day period or investments in the Company by collaborators that also simultaneously enter into agreements with the Company regarding the issuance of shares use of the Company's technologies, services or discoveries by such collaborator, provided that the number of shares of Common Stock following so issued, together with any shares of Common Stock issuable upon conversion, exercise or exchange of such 90 day securities, does not exceed an aggregate of 3,500,000 shares of Common Stock and provided further that the persons to whom such securities are issued execute a "lock-up" agreement substantially in the form of Exhibit A covering the period to a marketing, development or manufacturing collaborator will not violate ending 365 days after the terms date of this paragraphthe Prospectus.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $[______] a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of [1,050,000] Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments overallotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and hereof described in the Final Memorandum, Prospectus of which the Underwriters have been advised in writing or (DC) the issuance grant of additional stock options under pursuant to the Company's existing stock option plans, employee benefit plans described in the Prospectus provided that either these stock options do not become exercisable during the 180 day "lockup" period or the grantees of such stock options are not exercisable during have each entered into a "lockup" agreement substantially in the form of Exhibit A hereto, between you and such 90 day periodgrantee, or (E) relating to the issuance by the Company sales and certain other dispositions of shares of Common Stock pursuant or certain other securities, delivered to you on or before the Stock Purchase Agreement between date each such option is granted and which shall be in full force and effect on the Company and American Home Products Corporation, dated as date of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphgrant.

Agreements to Sell and Purchase. The Company hereby agrees to sell to ------------------------------- the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount of Firm Securities set forth in Schedule I hereto opposite its name at $______ a purchase price of 97% of the principal amount thereof share (the "Purchase Price") plus accrued interest, if any, the number of Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the Closing Datenumber of Firm Shares to be sold by the Company as the number of Firm Shares set forth in Schedule II hereto opposite the name of such Underwriter bears to the total number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees and the Selling Shareholder agree to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of ______________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I II hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company Each Seller hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, purchase or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, Shares to be sold hereunder or (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in writing. In addition, each Selling Shareholder agrees that, without the Final Memorandumprior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, (D) it will not, during the issuance period ending 180 days after the date of additional options under the Company's existing stock option plansProspectus, provided that such stock options are not exercisable during such 90 day periodmake any demand for, or (E) exercise any right with respect to, the issuance by the Company registration of any shares of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's or any security convertible into or exercisable or exchangeable for Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphStock.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $ a share (the Company “Purchase Price”) the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchase, severally and not jointly, up to $30,000,000 principal amount of Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇"), You may exercise this right on behalf of the Initial Purchasers, elects Underwriters in whole or from time to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ shall so notify the Company time in writing part by giving written notice not later than 30 days after the date of this Agreement, which . Any exercise notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such Each purchase date must be at least two business days after the written notice is given and may not be the same as the Closing Date but not earlier than the Closing Date closing date for the Firm Shares nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 6 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any On each day, if any, that Additional Securities Shares are to be purchasedpurchased (an “Option Closing Date”), each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased on such Option Closing Date as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ the Representatives on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock (such shares of Common Stock and such Securities, together the “MHG Co. Securities”) or (ii2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i1) or (ii2) above is to be settled by delivery of Common Stock or such other securitiesMHG Co. Securities, in cash or otherwiseotherwise or (3) file any registration statement with the Commission relating to the offering of any MHG Co. Securities (other than registration statement(s) on Form S-8 to register securities for issuance pursuant to the Company’s 2006 Omnibus Stock Incentive Plan described in the Time of Sale Prospectus). The foregoing sentence restrictions contained in the preceding paragraph shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and which the Underwriters have been advised in writing, (C) the issuance by the Company of MHG Co. Securities under the Company’s 2006 Omnibus Stock Incentive Plan described in the Final MemorandumTime of Sale Prospectus, (D) the issuance by the Company of additional options under shares of Common Stock as part of the Company's existing stock option plansFormation Transactions, provided that such stock options are not exercisable during such 90 day period, or and (E) the issuance by the Company of shares of Common Stock, or by the Operating Company of OC Units, as consideration for one or more acquisitions, provided that (i) the aggregate market value of all such shares of Common Stock, including shares of Common Stock pursuant issuable upon conversion of any such OC Units, does not exceed 10% of the market capitalization of the Company as of 4:30 p.m. (New York City time) on the Closing Date, and (ii) the recipients of any such shares of Common Stock or OC Units shall enter into a written agreement agreeing to the Stock Purchase Agreement between restrictions set forth in the preceding paragraph and this paragraph. Notwithstanding the foregoing, if (1) during the last 17 days of the 180-day restricted period the Company and American Home Products Corporationissues an earnings release; or (2) prior to the expiration of the 180-day restricted period, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company announces that it will release earnings results during such 90 the 16-day period regarding beginning on the last day of the 180-day period, the restrictions imposed by this agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of shares the earnings release. The Company shall promptly notify the Representatives of any earnings release that may give rise to an extension of the Company's Common Stock following such 90 initial 180-day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphrestricted period.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name names at U.S.$_____ a purchase price of 97% of the principal amount thereof share (the "Purchase PricePURCHASE PRICE") plus accrued interest, if any, to the Closing Date). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of __________ Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date or the fourth business day after the date of such notice, nor later than ten the tenth business days day after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-over- allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 180 days after the date of the Final MemorandumProspectus, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of which the Underwriters have been advised in writing, (C) the issuance of an aggregate of ____ shares of Common Stock to Biogen, Inc., Genentech Inc. and described the University of Florida Research Foundation, in each case on the terms set forth in the Final MemorandumProspectus, or (D) the issuance grant of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of to purchase Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following equity-based compensation plans described in the Prospectus, provided that such 90 options are not exercisable within such 180 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphperiod.

Agreements to Sell and Purchase. The Company hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Company the respective principal amount numbers of Firm Securities Shares set forth in Schedule I hereto opposite its name at $22.50125 a purchase price of 97% of the principal amount thereof share (the "“Purchase Price") plus accrued interest, if any, to the Closing Date”). On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time the right to purchasepurchase at any time and from time to time, severally and not jointly, up to $30,000,000 principal amount of 1,650,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm Securities. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The During the period commencing on the date hereof and ending on the 90th day following the date of the Prospectus, the Company hereby agrees thatwill not, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf Banc of America Securities LLC (“BAS”) and Citibank Global Markets Inc. (“Citi”) (which consent may be withheld at the Initial Purchasers, it will not, during the period ending 90 days after the date sole discretion of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose ofBAS and Citi), directly or indirectly, sell, offer, contract or grant any option to sell, pledge, transfer or establish an open “put equivalent position” or liquidate or decrease a “call equivalent position” within the meaning of Rule 16a-1(h) under the Exchange Act, or otherwise dispose of or transfer (or enter into any transaction which is designed to, or might reasonably be expected to, result in the disposition of), or announce the offering of, or file any registration statement under the Securities Act in respect of, any shares of Common Stock Stock, options or any securities convertible into or exercisable or exchangeable for warrants to acquire shares of the Common Stock or securities exchangeable or exercisable for or convertible into shares of Common Stock (ii) enter into any swap other than as contemplated by this Agreement with respect to the Shares); provided, however, that the Company may issue shares of its Common Stock or other arrangement that transfers options to another, in whole or in part, any of the economic consequences of ownership of the purchase its Common Stock, whether or Common Stock upon exercise of options, pursuant to any stock option, stock bonus or other stock plan or arrangement described in the Prospectus, but only if the holders of such shares, options, or shares issued upon exercise of such options, agree in writing not to sell, offer, dispose of or otherwise transfer any such transaction described in clause shares or options during such 90-day period without the prior written consent of BAS and Citi (i) or (ii) above is to which consent may be settled by delivery withheld at the sole discretion of Common Stock or such other securities, in cash or otherwiseBAS and Citi). The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company or Max Re Ltd. of shares of Common Stock or securities convertible into or exercisable or exchangeable for Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof of and described which the Underwriters have been advised in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, writing or (EB) the issuance by the Company or Max Re Ltd. of warrants to acquire Common Stock or securities convertible into or exercisable or exchangeable for shares of Common Stock pursuant to contractual agreements in effect on the Stock Purchase Agreement between date hereof of which the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphUnderwriters have been advised in writing.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $______ a share (the Company "PURCHASE PRICE") the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule Schedules I and II hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company agrees and the Selling Shareholder agree to sell to the Initial Purchasers U.S. Underwriters the Additional SecuritiesShares, and the Initial Purchasers U.S. Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount the number of Additional Securities Shares set forth opposite their name in Schedule I hereto at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")the U.S. Representatives, on behalf of the Initial PurchasersU.S. Underwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ the U.S. Representatives shall so notify the Company and the Selling Shareholder in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers U.S. Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser U.S. Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you the U.S. Representatives may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of U.S. Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser U.S. Underwriter bears to the total principal amount number of U.S. Firm Securities. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ on behalf of the Initial Purchasers, it will not, during the period ending 90 days after the date of the Final Memorandum, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (A) the sale of the Securities under this Agreement, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a security outstanding on the date of and described in the Final Memorandum, (D) the issuance of additional options under the Company's existing stock option plans, provided that such stock options are not exercisable during such 90 day period, or (E) the issuance by the Company of Common Stock pursuant to the Stock Purchase Agreement between the Company and American Home Products Corporation, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions by the Company during such 90 day period regarding the issuance of shares of the Company's Common Stock following such 90 day period to a marketing, development or manufacturing collaborator will not violate the terms of this paragraphShares.

Agreements to Sell and Purchase. The Company Each Seller, severally and not jointly, hereby agrees to sell to the several Initial PurchasersUnderwriters, and each Initial PurchaserUnderwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $38.68 a share (the Company "Purchase Price") the respective principal amount number of Firm Securities Shares (subject to such adjustments to eliminate fractional shares as you may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I hereto opposite its the name at a purchase price of 97% of the principal amount thereof (the "Purchase Price") plus accrued interest, if any, such Underwriter bears to the Closing Datetotal number of Firm Shares. On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Company MDP agrees to sell to the Initial Purchasers Underwriters the Additional SecuritiesShares, and the Initial Purchasers Underwriters shall have a one-time right to purchase, severally and not jointly, up to $30,000,000 principal amount of 10,500,000 Additional Securities Shares at the Purchase Price plus accrued interest, if any, to the date of payment and deliveryPrice. If ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated ("▇▇▇▇▇▇ ▇▇▇▇▇▇▇")you, on behalf of the Initial PurchasersUnderwriters, elects elect to exercise such option, ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ you shall so notify MDP and the Company in writing not later than 30 days after the date of this Agreement, which notice shall specify the principal amount number of Additional Securities Shares to be purchased by the Initial Purchasers Underwriters and the date on which such Additional Securities shares are to be purchased. Such date may be the same as the Closing Date (as defined below) but not earlier than the Closing Date nor later than ten five business days after the date of such notice. Additional Securities Shares may be purchased as provided in Section 4 5 hereof solely for the purpose of covering over-over- allotments made in connection with the offering of the Firm SecuritiesShares. If any Additional Securities Shares are to be purchased, each Initial Purchaser Underwriter agrees, severally and not jointly, to purchase the principal amount number of Additional Securities Shares (subject to such adjustments to eliminate fractional Securities shares as you may determine) that bears the same proportion to the total principal amount number of Additional Securities Shares to be purchased as the principal amount number of Firm Securities Shares set forth in Schedule I hereto opposite the name of such Initial Purchaser Underwriter bears to the total principal amount number of Firm SecuritiesShares. The Company hereby agrees that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Initial PurchasersUnderwriters, it will not, during the period ending 90 days after the date of the Final Memorandumthis Agreement, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The Selling Shareholders hereby agree that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, they and their respective subsidiaries (other than the Company) will not, during the period ending 90 days after the date of this Agreement, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The two foregoing sentence sentences shall not apply to (A) the sale of the Securities under this AgreementShares to be sold hereunder, (B) the issuance of the Underlying Securities upon conversion of the Securities, (C) the issuance by the Company of shares of Common Stock upon the exercise of an option or warrant or the conversion of a any convertible security outstanding on the date hereof of and described which the Underwriters have been advised in writing, (C) transactions by any person other than the Final MemorandumCompany relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the offering of the Shares, (D) the issuance by the Company of additional options under the Company's existing stock option plansup to 8,100,000 shares of Common Stock in connection with acquisitions or other strategic transactions, provided that such stock options these shares of Common Stock are not exercisable during such 90 day periodsubject to the lock-up restrictions described in this paragraph, or (E) the issuance by the Company of shares of Common Stock or options to purchase Common Stock to the Company's employees pursuant to the Stock Purchase Agreement between Company's stock option plan and employee stock purchase plan described in the Company and American Home Products CorporationProspectus, dated as of December 9, 1999. The Initial Purchasers acknowledge that discussions or (F) the issuance by the Company during such 90 day period regarding the issuance to AHP of shares of the Company's Common Stock following such on a quarterly basis pursuant to the provisions of the Governance Agreement. In addition, the Selling Shareholders, agree that, without the prior written consent of ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ & Co. Incorporated on behalf of the Underwriters, they will not, during the period ending 90 day period to a marketing, development or manufacturing collaborator will not violate days after the terms date of this paragraphAgreement, make any demand for, or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock.