EXHIBIT 10.5 
                              INVESTORS RIGHTS AGREEMENT
    This Agreement is made as of April 12, 1996 by and among Focal, Inc., a 
Delaware corporation (the "Company"), the holders of the Company's Series A, 
Series B, Series C, Series D and Series E Preferred Stock, the holders of 
certain warrants to purchase Preferred Stock of the Company and certain 
holders of Common Stock of the Company.  
                                       RECITALS
    A.   Simultaneously herewith, the Company is entering into a Series E 
Preferred Stock Purchase Agreement (the "1996 Series E Agreement") and 
issuing shares of Series E Preferred Stock to the Purchasers named in the 
Schedule of Investors to the 1996 Series E Agreement.  
    B.   In connection with this transaction, the Company wishes to 
consolidate the registration rights and rights of first refusal held by the 
holders of its Preferred Stock and warrants to acquire Preferred Stock into a 
single agreement. 
    NOW, THEREFORE, it is hereby agreed as follows:
1.       Certain Definitions.  As used in this Agreement, the following terms 
shall have the following respective meanings:
         "Commission" shall mean the Securities and Exchange Commission or 
any other federal agency at the time administering the Securities Act.
         "Conversion Stock" shall mean the shares of Common Stock issued or 
issuable upon conversion of the Shares.  
         "Holder" shall mean the holders of Registrable Securities, 
securities convertible into Registrable Securities or warrants to acquire 
Registrable Securities or securities convertible into Registrable Securities 
and any person holding such securities to whom the rights under this 
Agreement have been transferred in accordance with Section 2.13 hereof.
         "Initiating Holders" shall mean any Holder or Holders who in the 
aggregate hold or have the power to acquire (through conversion or exercise 
of other securities) at least 40% of the Registrable Securities.
         "Purchasers" shall mean the purchasers of Series A and B Preferred 
Stock pursuant to the Preferred Stock Purchase Agreement dated May 31, 1992 
(the "Series A and B Agreement"), the Purchasers of Series C Preferred Stock 
pursuant to the Series C Preferred Stock Purchase Agreement dated December 
22, 1992 (the "Series C Agreement"), the Purchasers of Series D Preferred 
Stock pursuant to the Series D Agreement dated August 11, 1993 (the "1993 
Series D Agreement") the
Purchasers of Series D Preferred Stock pursuant to the Series D Agreement 
dated August 5, 1994 (the "1994 Series D Agreement"), the Purchasers of 
Series E Preferred Stock pursuant to the 1996 Series E Agreement.  
         "Registrable Securities" means (i) the Conversion Stock, and (ii) 
any Common Stock of the Company issued or issuable with respect to, or in 
exchange for or in replacement of the Conversion Stock or other securities 
convertible into or exercisable for Conversion Stock upon any stock split, 
stock dividend, recapitalization, or similar event, provided, however, that 
shares of Common Stock or other securities shall only be treated as 
Registrable Securities for the purposes of Section 2.6 hereof if and so long 
as they have not been sold to or through a broker or dealer or underwriter in 
a public distribution or a public securities transaction.
         The terms "register," "registered" and "registration" refer to a 
registration effected by preparing and filing a registration statement in 
compliance with the Securities Act, and the declaration or ordering of the 
effectiveness of such registration statement.
         "Registration Expenses" shall mean all expenses, except as otherwise 
stated below, incurred by the Company in complying with Sections 2.5, 2.6 and 
2.7 hereof, including, without limitation, all registration, qualification 
and filing fees, printing expenses, escrow fees, fees and disbursements of 
counsel for the Company and special counsel to the selling Holders, blue sky 
fees and expenses, the expense of any special audits incident to or required 
by any such registration (but excluding the compensation of regular employees 
of the Company which shall be paid in any event by the Company).
         "Restricted Securities" shall mean the securities of the Company 
required to bear the legend set forth in Section 2.2 hereof.
         "Securities Act" shall mean the Securities Act of 1933, as amended, 
or any similar federal statute and the rules and regulations of the 
Commission thereunder, all as the same shall be in effect at the time.
         "Selling Expenses" shall mean all underwriting discounts, selling 
commissions and stock transfer taxes applicable to the securities registered 
by the Holders.
         "Shares" shall mean the shares of the Company's (i) Series A 
Preferred Stock and Series B Preferred Stock issued pursuant to the Series A 
and B Agreement, (ii) Series C Preferred Stock issued pursuant to the Series 
C Agreement, (iii) Series C Preferred Stock issued pursuant to a warrant held 
by Comdisco, Inc., (iv) Series D Preferred Stock issued or issuable pursuant 
to warrants held by Comdisco, Inc., MMC/GATX Partnership No. I, ▇▇▇▇▇▇▇ 
Investment Securities and Invemed Associates, (v) Series D Preferred Stock 
issued pursuant to the 1993 Series D Agreement and the 1994 Series D 
Agreement, and (v) Series E Preferred Stock issued pursuant to the 1996 
Series E Agreement. 
2.       Restrictions on Transferability of Securities;
         Compliance with Securities Act; Registration Rights
         a.        Restrictions on Transferability.  The Shares and the 
              Conversion Stock shall not be sold, assigned, transferred or 
              pledged except upon the conditions specified in this Section 2, 
              which conditions are intended to ensure compliance with the 
              provisions of the Securities Act.  The Purchasers will cause 
              any proposed purchaser, assignee, transferee, or pledgee of the 
              Shares or the Conversion Stock held by the Purchasers to agree 
              to take and hold such securities subject to the provisions and 
              upon the conditions specified in this Section 2.
         b.        Restrictive Legend.  Each certificate representing (i) the 
              Shares, (ii) the Conversion Stock and (iii) any other 
              securities issued in respect of the Shares or the Conversion 
              Stock upon any stock split, stock dividend, recapitalization, 
              merger, consolidation or similar event, shall (unless otherwise 
              permitted by the provisions of Section 2.3 below) be stamped or 
              otherwise imprinted with a legend in the following form (in 
              addition to any legend required under applicable state 
              securities laws): 
    THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR 
    INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933. 
    SUCH SHARES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SUCH 
    REGISTRATION UNLESS THE TRANSFER IS IN ACCORDANCE WITH RULE 144 OR 
    SIMILAR RULE OR UNLESS THE COMPANY RECEIVES AN OPINION OF COUNSEL 
    REASONABLY ACCEPTABLE TO IT STATING THAT SUCH SALE OR TRANSFER IS EXEMPT 
    FROM THE REGISTRATION AND PROSPECTUS DELIVERY REQUIREMENTS OF SAID ACT. 
    COPIES OF THE AGREEMENT COVERING THE PURCHASE OF THESE SHARES AND 
    RESTRICTING THEIR TRANSFER MAY BE OBTAINED AT NO COST BY WRITTEN REQUEST 
    MADE BY THE HOLDER OF RECORD OF THIS CERTIFICATE TO THE SECRETARY OF THE 
    CORPORATION AT THE PRINCIPAL EXECUTIVE OFFICES OF THE CORPORATION.
    The Purchasers and Holders consent to the Company making a notation on 
its records and giving instructions to any transfer agent of the Shares or 
the Conversion Stock in order to implement the restrictions on transfer 
established in this Section 2.
         c.        Notice of Proposed Transfers.  The holder of each 
              certificate representing Restricted Securities by acceptance 
              thereof agrees to comply in all respects with the provisions 
              of this Section 2.3.  Prior to any proposed sale, assignment, 
              transfer or pledge of any Restricted Securities (other than (i) 
              a transfer not involving a change in   beneficial ownership or 
              (ii) in transactions involving the distribution without 
              consideration of Restricted Securities by any Holder to any of 
              its partners, or retired partners, or to the estate of any of 
              its partners or 
              retired partners, (iii) a transfer to an affiliated fund, 
              partnership or company, which is not a competitor of the 
              Company, subject to compliance with applicable securities laws, 
              or (iv) transfers in compliance with Rule 144, so long as the 
              Company is furnished with satisfactory evidence of compliance 
              with such Rule), unless there is in effect a registration 
              statement under the Securities Act covering the proposed 
              transfer, the holder thereof shall give written notice to the 
              Company of such holder's intention to effect such transfer, 
              sale, assignment or pledge. Each such notice shall describe the 
              manner and circumstances of the proposed transfer, sale, 
              assignment or pledge in sufficient detail, and shall be 
              accompanied, at such holder's expense, by either (i) a written 
              opinion of legal counsel who shall, and whose legal opinion 
              shall be, reasonably satisfactory to the Company addressed to 
              the Company, to the effect that the proposed transfer of the 
              Restricted Securities may be effected without registration 
              under the Securities Act; or (ii) a "no action" letter from the 
              Commission to the effect that the transfer of such securities 
              without registration will not result in a recommendation by the 
              staff of the Commission that action be taken with respect 
              thereto, whereupon the holder of such Restricted Securities 
              shall be entitled to transfer such Restricted Securities in 
              accordance with the terms of the notice delivered by the holder 
              to the Company.  Each certificate evidencing the Restricted 
              Securities transferred as above provided shall bear, except if 
              such transfer is made pursuant to Rule 144, the appropriate 
              restrictive legend set forth in Section 2.2 above, except that 
              such certificate shall not bear such restrictive legend if in 
              the opinion of counsel for such holder and in the reasonable 
              opinion of the Company such legend is not required in order to 
              establish compliance with any provision of the Securities Act.
         d.        Removal of Restrictions on Transfer of Securities.  Any 
              legend referred to in Section 2.2 hereof stamped on a 
              certificate evidencing (i) the Shares, (ii) the Conversion 
              Stock or (iii) any other securities issued in respect of the 
              Shares or the Conversion Stock upon any stock split, stock 
              dividend, recapitalization, merger, consolidation or similar 
              event and the stock transfer instructions and record notations 
              with respect to such security shall be removed and the Company 
              shall issue a certificate without such legend to the holder of 
              such security if such security is registered under the 
              Securities Act, or if such holder provides the Company with an 
              opinion of counsel (which may be counsel for the Company) 
              reasonably acceptable to the Company to the effect that a 
              public sale or transfer of such security may be made without 
              registration under the Securities Act or such holder provides 
              the Company with reasonable assurances,which may, at the option 
              of the Company, include an opinion of counsel satisfactory to 
              the Company, that such security can be sold pursuant to Section 
              (k) of 
              Rule 144 under the Securities Act. The Company will cause 
              legend removal to be authorized or provide a written response 
              as to why legends may not be removed within 10 days of receipt 
              of any such request. 
         e.        Requested Registration.
    i.        Request for Registration.  In case the Company shall receive 
          from Initiating Holders a written request that the Company effect 
          any registration, qualification or compliance with respect to 
          shares of Registrable Securities with an expected aggregate 
          offering price to the public of at least $5,000,000, the Company 
          will: 
         (1)       within ten days of the receipt by the Company of such 
              notice, give written notice of the proposed registration, 
              qualification or compliance to all other Holders; and
         (2)       as soon as practicable, use its best efforts to effect 
              such registration, qualification or compliance (including, 
              without limitation, appropriate qualification under applicable 
              blue sky or other state securities laws and appropriate 
              compliance with applicable regulations issued under the 
              Securities Act and any other governmental requirements or 
              regulations) as may be so requested and as would permit or 
              facilitate the sale and distribution of all or such portion of 
              such Registrable Securities as are specified in such request, 
              together with all or such portion of the Registrable Securities 
              of any Holder or Holders joining in such request as are 
              specified in a written request received by the Company within 
              20 days after receipt of such written notice from the Company; 
    Provided, however, that the Company shall not be obligated to take any 
action to effect any such registration, qualification or compliance pursuant 
to this Section 2.5:
              (a)       In any particular jurisdiction in which the Company 
                   would be required to execute a general consent to service 
                   of process in effecting such registration, qualification 
                   or compliance unless the Company is already subject to 
                   service in such jurisdiction and except as may be required 
                   by the Securities Act; 
              (b)       Prior to the earlier of (i) December 31, 1997 or (ii) 
                   the expiration of six months following completion of the 
                   Company's first registered public offering of its stock; 
              (c)       During the period starting with the date sixty (60) 
                   days prior to the Company's estimated date of filing of, 
                   and ending on the date three (3) months immediately 
                   following the effective date of, any registration 
                   statement pertaining to securities of the Company (other 
                   than a registration of securities in a Rule 145 
                   transaction, with respect to an employee benefit plan or 
                   with respect to the Company's first registered public 
                   offering of its stock), provided that the Company is 
                   actively employing in good faith all reasonable efforts to 
                   cause such registration statement to become effective; 
              (d)       After the Company has effected two such registrations 
                   pursuant to this Section 2.5(a) covering all shares 
                   requested to be registered by the Holders initiating or 
                   joining such request, and such registrations have been 
                   declared or ordered effective, and, if the method of 
                   disposition specified by such initiating or requesting 
                   Holders shall have been a firm commitment underwritten 
                   public offering, all such shares shall have been sold 
                   pursuant thereto; 
              (e)       If the Company shall furnish to such Holders a 
                   certificate signed by the President of the Company stating 
                   that in the good faith judgment of the Board of Directors 
                   it would be seriously detrimental to the Company or its 
                   stockholders for a registration statement to be filed in 
                   the near future, then the Company's obligation to use its 
                   best efforts to register, qualify or comply under this 
                   Section 2.5 shall be deferred for a period not to exceed 
                   90 days from the date of receipt of written request from 
                   the Initiating Holders; provided, however, that the 
                   Company shall not exercise such right more than once in 
                   any twelve-month period.
    Subject to the foregoing clauses (A) through (E), the Company shall file 
a registration statement covering the Registrable Securities so requested to 
be registered as soon as practicable, after receipt of the request or 
requests of the Initiating Holders.
         ii.       Underwriting.  In the event that a registration pursuant 
              to Section 2.5 is for a registered public offering involving an 
              underwriting, the Company shall so advise the Holders as part 
              of the notice given pursuant to Section 2.5(a)(i).  In such 
              event, the right of any Holder to registration pursuant to 
              Section 2.5 shall be conditioned upon such Holder's 
              participation in the  underwriting arrangements required by 
              this Section 2.5, and the inclusion of such Holder's 
              Registrable Securities in the underwriting to the extent 
              requested shall be limited to the extent provided herein.
    The Company shall (together with all Holders proposing to distribute 
their securities through such underwriting) enter into an underwriting 
agreement in customary form with the managing  underwriter of recognized 
national standing selected for such  underwriting by the Company and 
reasonably acceptable to a majority of the Holders proposing to distribute 
their securities through such underwriting; provided, however, that if 
General Electric Pension Trust ("GEPT") is participating in such underwriting 
and the General Electric Company is directly or indirectly the beneficial 
owner of five percent (5%) or more of the outstanding equity interests of any 
underwriter or underwriters, GEPT shall have the absolute right to disapprove 
such underwriter or underwriters. Notwithstanding any other provision of this 
Section 2.5, if the managing underwriter advises the Initiating Holders in 
writing that marketing factors require a limitation of the number of shares 
to be underwritten, then the Company shall so advise all holders of 
Registrable Securities and the number of shares of Registrable Securities 
that may be included in the registration and underwriting shall be allocated 
among all Holders thereof in proportion, as nearly as practicable, to the 
respective amounts of Registrable Securities requested by such Holders to be 
included in such registration statement or in such other manner as shall be 
agreed to by the Company and Holders of a majority of the Registrable 
Securities proposed to be included in such registration.  No Registrable 
Securities excluded from the underwriting by reason of the underwriter's 
marketing limitation shall be included in such registration.  To facilitate 
the allocation of shares in accordance with the above provisions, the Company 
or the underwriters may round the number of shares allocated to any Holder to 
the nearest 100 shares.
    If any Holder of Registrable Securities disapproves of the terms of the 
underwriting, such Holder may elect to withdraw therefrom by written notice 
to the Company, the managing underwriter and the Initiating Holders.  The 
Registrable Securities and/or other securities so withdrawn shall also be 
withdrawn from registration, and such Registrable Securities shall not be 
transferred in a public distribution prior to 90 days after the effective 
date of such registration, or such other shorter period of time as the 
underwriters may require.
         f.        Company Registration.
    i.        Notice of Registration.  If at any time or from time to time 
         the Company shall determine to register any of its securities, 
         either for its own account or the account of a security holder or 
         holders, other than (i) a registration relating solely to employee 
         benefit plans or (ii) a registration relating solely to a Commission 
         Rule 145 transaction, the Company will: 
         (1)       promptly give to each Holder written notice thereof; and 
         (2)       include in such registration (and any related 
              qualification under blue sky laws or other compliance), and in 
              any underwriting involved therein, all the Registrable 
              Securities specified in a written request or requests, made 
              within 20 days after receipt of such written notice from the 
              Company, by any Holder.
    ii.       Underwriting.  If the registration of which the Company gives 
         notice is for a registered public offering involving an 
         underwriting, the Company shall so advise the Holders as a part of 
         the written notice given pursuant to Section 2.6(a)(i); provided, 
         however, that if GEPT is participating in such underwriting and the 
         General Electric Company is directly or indirectly the beneficial 
         owner of five percent (5%) or more of the outstanding equity 
         interests of any underwriter or underwriters, GEPT shall have the 
         absolute right to disapprove such underwriter or underwriters.  In 
         such event the right of any Holder to registration pursuant to 
         Section 2.6 shall be conditioned upon such Holder's participation in 
         such underwriting and the inclusion of Registrable Securities in the 
         underwriting to the extent provided herein.  All Holders proposing 
         to distribute their securities through such underwriting shall 
         (together with the Company) enter into an underwriting agreement in 
         customary form with the managing underwriter selected for such 
         underwriting by the Company.  Notwithstanding any other provision of 
         this Section 2.6, if the managing underwriter determines that 
         marketing factors require a limitation of the number of shares to be 
         underwritten, the managing underwriter may limit the Registrable 
         Securities and other securities to be distributed through such 
         underwriting; provided, however, that except in connection with the 
         Company's initial underwritten public offering of Common Stock the 
         number of Registrable Securities shall not be limited to less than 
         20% of the aggregate number of shares proposed to be included in 
         such underwriting.  The Company shall so advise all Holders 
         distributing their securities through such underwriting of such 
         limitation and the number of shares of Registrable Securities that 
         may be included in the registration (and underwriting if any) shall 
         be allocated among all Holders in proportion, as nearly as 
         practicable, to the respective amounts of Registrable Securities 
         requested by such Holders to be included in such Registration 
         Statement.  To facilitate the allocation of shares in accordance 
         with the above provisions, the Company may round the number of 
         shares allocated to any Holder or holder to the nearest 100 shares. 
         If any Holder or holder disapproves of the terms of any such 
         underwriting, such Holder or holder may elect to withdraw therefrom 
         by written notice to the Company and the managing underwriter.  Any 
         securities excluded or withdrawn from such underwriting shall be 
         withdrawn from such registration, and shall not be transferred in a 
         public distribution prior to 90 days after the effective date of the 
         registration statement relating thereto, or such other shorter 
         period of time as the underwriters may require. 
    iii.      Right to Terminate Registration.  The Company shall have the 
         right to terminate or withdraw any registration initiated by it 
         under this Section 2.6 prior to the effectiveness of such 
         registration whether or not any Holder has elected to include 
         securities in such registration.  The Registration Expenses of such 
         withdrawn registration shall be borne by the Company in accordance 
         with Section 2.8 hereof. 
         g.        Registration on Form S-3.
    i.        If any Holder or Holders request that the Company file a 
         registration statement on Form S-3 (or any successor form to Form 
         S-3), or any similar short-term registration statement, for a public 
         offering of Registrable Securities, the reasonably anticipated 
         aggregate price to the public of which, net of underwriting 
         discounts and commissions (if any), would exceed $1,000,000 and the 
         Company is a registrant entitled to use Form S-3 to register the 
         Registrable Securities for such an offering, the Company shall use 
         its best efforts to cause such Registrable Securities to be 
         registered on such form for the offering and to cause such 
         Registrable Securities to be qualified in such jurisdictions as the 
         Holder or Holders may reasonably request; provided, however, that 
         the Company shall not be required to effect more than four 
         registrations pursuant to this Section 2.7 or more than one such 
         registration in any twelve (12) month period.  After the Company's 
         first public offering of its securities, the Company will use its 
         best efforts to qualify for Form S-3 registration or a similar 
         short-form registration.  The provisions of Section 1.6(b) shall be 
         applicable to each registration initiated under this Section 2.7. 
    ii.       Notwithstanding the foregoing, the Company shall not be 
         obligated to take any action pursuant to this Section 2.7: (i) in 
         any particular jurisdiction in which the Company would be required 
         to execute a general consent to service of process in effecting such 
         registration, qualification or compliance unless the Company is 
         already subject to service in such jurisdiction and except as may be 
         required by the Securities Act; (ii) if the Company, within ten (10) 
         days of the receipt of the request of the initiating Holders, gives 
         notice of its bona fide intention to effect the filing of a 
         registration statement with the Commission within ninety (90) days 
         of receipt of such request (other than with respect to a 
         registration statement relating to a Rule 145 transaction, or an 
         offering solely to employees); (iii) during the period starting with 
         the date sixty (60) days prior to the Company's estimated date of 
         filing of, and ending on the date three (3) months immediately 
         following, the effective date of any registration statement 
         pertaining to securities of the Company (other than a registration 
         of securities in a Rule 145 transaction or with respect to an 
         employee benefit plan), provided that the Company is actively 
         employing in good faith all reasonable efforts to cause such 
         registration statement to become effective; or (iv) if the Company 
         shall furnish to such Holder a certificate signed by the President 
         of the Company stating that in the good faith judgment of the Board 
         of Directors it would be seriously detrimental to the Company or its 
         stockholders for registration statements to be filed in the near 
         future, then the Company's obligation to use its best efforts to 
         file a registration statement shall be deferred for a period not to 
         exceed 90 days from the receipt of the request to file such 
         registration by such Holder; 
         provided, however, that the Company shall not exercise such right 
         more than once in any twelve-month period.
         h.        Expenses of Registration.  All Registration Expenses 
              incurred in connection with registrations pursuant to Sections 
              2.5, 2.6 and 2.7 shall be borne by the Company. All Selling 
              Expenses relating to securities registered on behalf of the 
              Holders shall be borne by the holders of securities included in 
              such registration pro rata with the Company and among each 
              other on the basis of the number of shares so registered.
         i.        Registration Procedures.  In the case of each 
              registration, qualification or compliance effected by the 
              Company pursuant to this Section 2, the Company will keep each 
              Holder advised in writing as to the initiation of each 
              registration, qualification and compliance and as to the 
              completion thereof.  At its expense the Company will: 
    i.        Prepare and file with the Commission a registration statement 
         with respect to such securities and use its best efforts to cause 
         such registration statement to become and remain effective for at 
         least one hundred eighty (180) days or until the distribution 
         described in the Registration Statement has been completed;
    ii.       Prepare and file with the Commission such amendments and 
         supplements to such registration statement and the prospectus used 
         in connection with such registration statement as may be necessary 
         to comply with the provisions of the Securities Act with respect to 
         the disposition of all securities covered by such registration 
         statement. 
    iii.      Furnish to the Holders participating in such registration and 
         to the underwriters of the securities being registered such 
         reasonable number of copies of the registration statement, 
         preliminary prospectus, final prospectus and such other documents as 
         such underwriters may reasonably request in order to facilitate the 
         public offering of such securities. 
    iv.       Furnish, at the request of any Holder requesting registration 
         of Registrable Securities at the time such securities are delivered 
         to the underwriters (if any) for sale in connection with a 
         registration pursuant to this Section 2.9, (i) an opinion, dated 
         such date, of the counsel representing the Company for the purposes 
         of such registration, in form and substance as is customarily given 
         to underwriters in an underwritten public offering, addressed to the 
         underwriters, if any, and to the Holders requesting registration of 
         Registrable Securities and (ii) a letter dated the date of 
         commencement of the offering and a "bring-down" letter dated as of 
         the 
         closing date of such offering, from the independent accountants of 
         the Company, in form and substance as is customarily given by 
         independent accountants to underwriters in an underwritten public 
         offering, addressed to the underwriters, if any, and to the Holders 
         requesting registration of Registrable Securities. 
         j.        Indemnification.
    i.        The Company will indemnify each Holder, each of its officers, 
         directors, partners and legal counsel, and each person controlling 
         (or deemed to be controlling) such Holder within the meaning of 
         Section 15 of the Securities Act, with respect to which 
         registration, qualification or compliance has been effected pursuant 
         to this Section 2, and each underwriter, if any, and each person who 
         controls any underwriter within the meaning of Section 15 of the 
         Securities Act, against all expenses, claims, losses, damages or 
         liabilities (or actions in respect thereof), including any of the 
         foregoing incurred in settlement of any litigation, commenced or 
         threatened, arising out of or based on any untrue statement (or 
         alleged untrue statement) of a material fact contained in any 
         registration statement, prospectus, offering circular or other 
         document, or any amendment or supplement thereto, incident to any 
         such registration, qualification or compliance, or based on any 
         omission (or alleged omission) to state therein a material fact 
         required to be stated therein or necessary to make the statements 
         therein, in light of the circumstances in which they were made, not 
         misleading, or any violation by the Company of the Securities Act or 
         any rule or regulation promulgated under the Securities Act 
         applicable to the Company in connection with any such registration, 
         qualification or compliance, and the Company will reimburse each 
         such Holder, each of its officers, directors, partners and legal 
         counsel and each person controlling such Holder, each such 
         underwriter and each person who controls any such underwriter, for 
         any legal and any other expenses reasonably incurred in connection 
         with investigating, preparing or defending any such claim, loss, 
         damage, liability or action, provided that the Company will not be 
         liable in any such case to the extent that any such claim, loss, 
         damage, liability or expense arises out of or is based on any untrue 
         statement or omission or alleged untrue statement or omission, made 
         in reliance upon and in conformity with written information 
         furnished to the Company by an instrument duly executed by such 
         Holder, controlling person or underwriter and stated to be 
         specifically for use therein. 
    ii.       Each Holder will, if Registrable Securities held by such Holder 
         are included in the securities as to which such registration, 
         qualification or compliance is being effected, indemnify the 
         Company, each of its directors, officers and legal counsel, each 
         underwriter, if any, of the Company's securities covered by such a 
         registration statement, each person who controls the Company or such 
         underwriter within the meaning of Section 15 of the Securities Act, 
         and each other Holder, each of its officers, directors, partners 
         and legal counsel and each person controlling such Holder within the 
         meaning of Section 15 of the Securities Act, against all claims, 
         losses, damages and liabilities (or actions in respect thereof) 
         arising out of or based on any untrue statement (or alleged untrue 
         statement) of a material fact contained in any such registration 
         statement, prospectus, offering circular or other document, or any 
         omission (or alleged omission) to state therein a material fact 
         required to be stated therein or necessary to make the statements 
         therein not misleading, and will reimburse the Company, such 
         Holders, such directors, officers, persons, underwriters or control 
         persons for any legal or any other expenses reasonably incurred in 
         connection with investigating or defending any such claim, loss, 
         damage, liability or action, in each case to the extent, but only to 
         the extent, that such untrue statement (or alleged untrue statement) 
         or omission (or alleged omission) is made in such registration 
         statement, prospectus, offering circular or other document in 
         reliance upon and in conformity with written information furnished 
         to the Company by an instrument duly executed by such Holder and 
         stated to be specifically for use therein.  Notwithstanding the 
         foregoing, the liability of each Holder under this subsection (b) 
         shall be limited to the proportion of any such loss, claim, damage, 
         liability or expense which is equal to the proportion that the 
         public offering price of the shares sold by such Holder under such 
         registration statement bears to the total public offering price of 
         all securities sold thereunder, but not to exceed the proceeds 
         received by such Holder from the sale of Registrable Securities 
         covered by such registration statement.  A Holder will not be 
         required to enter into any agreement or undertaking in connection 
         with any registration under this Section 2 providing for any 
         indemnification or contribution on the part of such Holder greater 
         than the Holder's obligations under this Section 2.10(b). 
    iii.      Each party entitled to indemnification under this Section 2.10 
         (the "Indemnified Party") shall give notice to the party required to 
         provide indemnification (the "Indemnifying Party") promptly after 
         such Indemnified Party has actual knowledge of any claim as to which 
         indemnity may be sought, and shall permit the Indemnifying Party to 
         assume the defense of any such claim or any litigation resulting 
         therefrom, provided that counsel for the Indemnifying Party, who 
         shall conduct the defense of such claim or litigation, shall be 
         approved by the Indemnified Party (whose approval shall not 
         unreasonably be withheld), and the Indemnified Party may participate 
         in such defense at such party's expense, and provided further that 
         the failure of any Indemnified Party to give notice as provided 
         herein shall not relieve the Indemnifying Party of its obligations 
         under this Section 2 unless the failure to give such notice is 
         materially prejudicial to an Indemnifying Party's ability to defend 
         such action and provided further, that the Indemnifying Party shall 
         not assume the defense for matters as to which there is a conflict 
         of interest or separate and different defenses but shall bear the 
         expense of such defense nevertheless.  No Indemnifying Party, in the 
         defense of any such claim or 
         litigation, shall, except with the consent of each Indemnified 
         Party, consent to entry of any judgment or enter into any settlement 
         which does not include as an unconditional term thereof the giving 
         by the claimant or plaintiff to such Indemnified Party of a release 
         from all liability in respect to such claim or litigation. 
    iv.       If the indemnification provided for paragraphs (a) through (c) 
         of this Section 2.10 is unavailable or insufficient to hold harmless 
         an indemnified party under such paragraphs in respect of any losses, 
         claims, damages or liabilities or actions in respect thereof 
         referred to therein, then each indemnifying party shall in lieu of 
         indemnifying such indemnified party contribute to the amount paid or 
         payable by such indemnified party as a result of such losses, 
         claims, damages, liabilities or actions in such proportion as 
         appropriate to reflect the relative fault of the Company, on the one 
         hand, and the underwriters and the Holder of such Registrable 
         Securities, on the other, in connection with the statements or 
         omissions which resulted in such losses, claims, damages, 
         liabilities or actions as well as any other relevant equitable 
         considerations, including the failure to give any notice under 
         paragraph (c).  The relative fault shall be determined by reference 
         to, among other things, whether the untrue or alleged untrue 
         statement of a material fact relates to information supplied by the 
         Company, on the one hand, or the underwriters or the Holders of such 
         Registrable Securities, on the other, and to the parties' relative 
         intent, knowledge, access to information and opportunity to correct 
         or prevent such statement or omission.  The Company and each of the 
         Holders agrees that it would not be just and equitable if 
         contributions pursuant to this paragraph were determined by pro rata 
         allocation (even if all of the Holders of such Registrable 
         Securities were treated as one entity for such purpose) or by any 
         other method of allocation which did not take account of the 
         equitable considerations referred to above in this paragraph.  The 
         amount paid or payable by an indemnified party as a result of the 
         losses, claims, damages, liabilities or action in respect thereof, 
         referred to above in this paragraph, shall be deemed to include any 
         legal or other expenses reasonably incurred by such indemnified 
         party in connection with investigating or defending any such action 
         or claim.  Notwithstanding the provisions of this paragraph, no 
         Holder shall be required to contribute any amount in excess of the 
         lesser of (i) the proportion that the public offering price of 
         shares sold by such Holder under such registration statement bears 
         to the total public offering price of all securities sold 
         thereunder, but not to exceed the proceeds received by such Holder 
         for the sale of Registrable Securities covered by such registration 
         statement and (ii) the amount of any damages which they would have 
         otherwise been required to pay by reason of such untrue or alleged 
         untrue statement or omission.  No person guilty of fraudulent 
         misrepresentations (within the meaning of Section 11(f) of the 
         Securities Act), shall be entitled to contribution from any person 
         who is not guilty of such fraudulent misrepresentation.
              k.        Information by Holder.  The Holder or Holders of 
                   Registrable Securities included in any registration shall 
                   furnish to the Company such information regarding such 
                   Holder or Holders, the Registrable Securities held by them 
                   and the distribution proposed by such Holder or Holders as 
                   the Company may reasonably request in writing and as shall 
                   be required in connection with any registration, 
                   qualification or compliance referred to in this Section 2. 
              l.        Rule 144 Reporting.  With a view to making available 
                   the benefits of certain rules and regulations of the 
                   Commission which may at any time permit the sale of the 
                   Restricted Securities to the public without registration, 
                   after such time as a public market exists for the Common 
                   Stock of the Company, the Company agrees to use its best 
                   efforts to: 
     i.       Make and keep public information available, as those terms are 
         understood and defined in Rule 144 under the Securities Act, at all 
         times after the effective date that the Company becomes subject to 
         the reporting requirements of the Securities Act or the Securities 
         Exchange Act of 1934, as amended. 
    ii.       Use its best efforts to file with the Commission in a timely 
         manner all reports and other documents required of the Company under 
         the Securities Act and the Securities Exchange Act of 1934, as 
         amended (at any time after it has become subject to such reporting 
         requirements); 
    iii.      So long as a Purchaser owns any Restricted Securities to 
         furnish to the Purchaser forthwith upon request a written statement 
         by the Company as to its compliance with the reporting requirements 
         of said Rule 144 (at any time after 90 days after the effective date 
         of the first registration statement filed by the Company for an 
         offering of its securities to the general 
         public), and of the Securities Act and the Securities Exchange 
         Act of 1934 (at any time after it has become subject to such 
         reporting requirements), a copy of the most recent annual or 
         quarterly report of the Company, and such other reports and 
         documents of the Company and other information in the possession 
         of or reasonably obtainable by the Company as a Purchaser may 
         reasonably request in availing itself of any rule or regulation 
         of the Commission allowing a Purchaser to sell any such     
         securities without registration.
         m.        Transfer of Registration Rights.  The rights to cause 
              the Company to register securities granted Holders under 
              Sections 2.5, 2.6 and 2.7 may be assigned to a transferee or
              assignee in connection with any transfer or assignment of 
              Registrable Securities by a Holder of not less than 100,000 
              shares of Registrable Securities, or to any transferee
              or assignee who is a constituent partner of a Holder or the 
              estate of such constituent partner, provided that such 
              transfer may otherwise be effected in accordance with  
              applicable securities laws.
         n.        Standoff Agreement.  Each Holder agrees in connection 
              with the Company's initial public offering of the Company's 
              securities, upon request of the Company or the underwriters 
              managing any underwritten offering of the Company's    
              securities, not to sell, make any short sale of, loan, grant
              any option for the purchase of, or otherwise dispose of any 
              Registrable Securities (other than those included in the 
              registration) without the prior written consent of the 
              Company or such underwriters, as the case may be, for such 
              period of time (not to exceed one hundred eighty (180) days)
              from the effective date of such registration as may be 
              requested by the underwriters; provided, that the officers 
              and directors of the Company who own stock of the Company 
              and all other holders of 5% or more of the Company's   
              outstanding Common Stock equivalents also agree to such 
              restrictions.
         o.        Rule 144A Information.  Whenever the Company receives a
              request for the following information from Initiating  
              Holders on or after December 31, 1997, then the Company 
              shall within 60 days after the date of such request provide 
              the information required in Rule 144A(d)(4) to such    
              Initiating Holders and any person or persons designated by 
              the Initiating Holders as a prospective buyer in a     
              transaction pursuant to Rule 144A.  The Company's      
              obligations pursuant to this Section 2.15 shall extend to 
              any person who acquires shares of the Company's Preferred 
              Stock and/or Conversion Stock as a result of a transaction 
              pursuant to Rule 144A.
         p.        Termination of Registration Rights.  The rights granted
              under this Section 2 shall terminate on the fifth      
              anniversary of the consummation of the initial underwritten 
              public offering of the Company's securities pursuant to a 
              registration statement filed under the Securities Act.
         
3.       Purchasers' Right of First Refusal.
              a.        Right of First Refusal Upon Issuances of Securities by 
                   the Company.  
         i.        The Company hereby grants, on the terms set forth in 
              this Section 3.1, to each Purchaser the right of first 
              refusal to purchase all or any part of such Purchaser's pro 
              rata share of the New Securities (as defined in Section 
              3.1(b)) which the Company may, from time to time, propose to
              sell and issue.  The 
              Purchasers may purchase said New  
              Securities on the same terms and at the same price at which 
              the Company proposes to sell the New Securities.  The pro 
              rata share of each Purchaser, for purposes of this right of
              first refusal, is the ratio of the total number of shares of
              Common Stock held by such Purchaser, including any shares of
              Common Stock into which shares of Preferred Stock held by 
              such Purchaser are convertible, to the total number of 
              shares of Common Stock outstanding immediately prior to the 
              issuance of the New Securities (including any shares of 
              Common Stock into which outstanding shares of Preferred 
              Stock are convertible).
         ii.       "New Securities" shall mean any capital stock of the 
              Company, whether now authorized or not, and any rights, 
              options or warrants to purchase said capital stock, and 
              securities of any type whatsoever that are, or may become, 
              convertible into said capital stock; provided that "New 
              Securities" does not include the following issuances (as 
              long as they are approved by the Company's board of    
              directors): (i) the Shares purchased under this Agreement or
              the Conversion Stock, (ii) securities offered pursuant to a 
              registration statement filed under the Securities Act, as 
              hereinafter defined, (iii) securities issued pursuant to the
              acquisition of another corporation by the Company by merger,
              purchase of substantially all of the assets or other   
              reorganization, (iv) up to 4,250,000 shares of Common Stock 
              or other securities hereafter issued or issuable to    
              officers, directors, employees, scientific advisors or 
              consultants of the Company pursuant to any employee or 
              consultant stock offering, plan or arrangement approved by 
              the Board of Directors of the Company, (v) all shares of 
              Common Stock or other securities hereafter issued in   
              connection with or as consideration for acquisition or 
              licensing of technology, (vi) all shares of Common Stock or 
              other securities hereafter issued pursuant to warrants, 
              rights or options, provided that the rights of first refusal
              established hereby applied to the initial sale or grant by 
              the Company of such warrants, rights or options, and   
              (vii) all shares of Common Stock or other securities issued 
              in connection with equipment leasing or equipment financing 
              arrangements.
         iii.      In the event the Company proposes to undertake an 
              issuance of New Securities, it shall give to the Purchasers 
              written notice (the "Notice") of its intention, describing 
              the type of New Securities, the price, the terms upon which 
              the Company proposes to issue the same, and a statement as 
              to the number of days from receipt of such Notice within 
              which the Purchasers must respond to such Notice.  The 
              Purchasers shall have thirty (30) days from the date of 
              receipt of the Notice to purchase any or all of the New 
              Securities for the price and upon the terms specified in the
              Notice by giving written notice to the Company and stating 
              therein the quantity of New Securities to be purchased and 
              forwarding payment for such New Securities to the Company if
              immediate payment is required by such terms, or in any event
              no later than thirty (30) days after the date of receipt of 
              the Notice.
         iv.       In the event the Purchasers fail to exercise in full 
              the right of first refusal within said thirty (30) day 
              period, the Company shall have ninety (90) days thereafter 
              to sell or enter into an agreement (pursuant to which the 
              sale of New Securities covered thereby shall be closed, if 
              at all, within thirty (30) days from date of said agreement)
              to sell the New Securities respecting which the Purchasers' 
              rights were not exercised, at a price and upon general terms
              no more favorable to the Purchasers thereof than specified 
              in the Notice.  In the event the Company has not sold the
              New Securities within said ninety (90) day period (or sold 
              and issued New Securities in accordance with the foregoing 
              within thirty (30) days from the date of said agreement), 
              the Company shall not thereafter issue or sell any New 
              Securities without first offering such securities to the 
              Purchasers in the manner provided above.
         v.        The right of first refusal granted under this     
              Section 3.1 shall expire upon:
              (1)       The date upon which a registration statement filed
                   by the Company under the Securities Act (other than a 
                   registration of securities in a Rule 145 transaction or
                   with respect to an employee benefit plan) in connection
                   with an underwritten public offering of its securities 
                   first becomes effective and the securities registered 
                   thereunder are sold.
              (2)       For each Purchaser, the date on which such   
                   Purchaser no longer holds a minimum of 75,000 Shares or
                   Conversion Stock or the number of Shares or Conversion 
                   Shares originally purchased, whichever is less.
              b.        Right of First Refusal Upon Issuances of     
                   Securities by the Company.  The right of first refusal 
                   granted under this Section is assignable by any   
                   Purchaser to any transferee of a minimum of 75,000 
                   Shares or Conversion Stock or to any transferee who is 
                   a constituent partner or affiliate of the transferor.
         
4.       Right of Co-Sale.
         ▇.   ▇▇▇▇▇ of Co-Sale Rights.
              (a)  If a Stockholder or a Purchaser proposes to sell or transfer
any shares of Common Stock now owned by the selling Stockholder or Purchaser
(the shares subject to such offer to be hereafter called the "Stock" and the
selling Stockholder or Purchaser to be called the "Selling Party") in one or
more related transactions, then, such Party shall promptly deliver written
notice (the "Co-Sale Notice") to each of the Purchasers (if such Selling Party
is a Stockholder) or to each of the other Purchasers (if such Selling Party is
an Purchaser) at least twenty (20) days prior to 
the closing of such sale or transfer.  For purposes of this Section 4, 
"Common Stock" shall mean (i) the Company's Common Stock (including 
Conversion Shares), (ii) shares of Common Stock issuable upon exercise of 
outstanding options and (iii) shares of Common Stock issuable upon conversion 
of the Shares or any other outstanding convertible securities.  The Co-Sale 
Notice shall describe in reasonable detail the proposed sale or transfer 
including, without limitation, the number of shares of Stock to be sold or 
transferred, the nature of such sale or transfer, the consideration to be 
paid and the name and address of each prospective purchaser or transferee.
              (b)  Each Purchaser shall have the right, exercisable upon
written notice to such Selling Party within thirty (30) days after receipt of
the Notice, to participate in such sale of Stock on the same terms and
conditions provided that no Purchaser shall be required to make any
representation or warranties or perform any undertakings other than with respect
to its title and authority.  To the extent one or more of the Purchasers
exercise such right of participation in accordance with the terms and conditions
set forth below, the number of shares of Stock that the Selling Party may sell
in the transaction shall be correspondingly reduced.
              (c)  Each Purchaser who elects to participate in a sale of Stock
under this Section 4 (a "Participant") may sell all or any part of that number
of shares of Stock equal to the product obtained by multiplying (i) the
aggregate number of shares of Stock covered by the Co-Sale Notice by (ii) a
fraction the numerator of which is the number of shares of Common Stock (on a
fully-diluted, as converted basis) owned by the Purchaser at the time of the
sale or transfer and the denominator of which is the total number of shares of
Common Stock owned by the Stockholders and Purchasers (including the Selling
Party) at the time of the sale or transfer.
              (d)  If any Purchaser fails to elect to fully participate in the
Selling Party's sale pursuant to this Section 4.1, the Selling Party shall
promptly give notice of such failure and the aggregate number of shares that the
non-participating Purchasers did not elect to sell (the "Unsold Portion") to
each of the Participants.  Such notice may be made by telephone if confirmed in
writing within fifteen (15) days.  The Participants shall have two (2) days from
the date such notice was given to agree to sell their pro rata share of the
Unsold Portion.  After the expiration of the fifteen (15) day period following
the provision of notice to the Participants and without being subject to the
provisions of this paragraph 4.1(d), the Selling Party shall have the right to
sell or transfer the number of shares of Stock that is equivalent to the balance
of the Unsold Portion that is not elected to be sold by the Participants.  For
purposes of this paragraph, a Participant's pro rata share shall be the ratio of
(x) the number of shares of Common Stock held by such Participant to (y) the
total number of shares of Common Stock held by all the Participants and the
Selling Party.
              (e)  Each Participant shall effect its participation in the sale
by promptly delivering to the Selling Party for transfer to the prospective
purchaser one or more certificates, properly endorsed for transfer, which
represent:
                   (i)  the type and number of shares of Common Stock
which such Participant elects to sell; or
                   (ii) that number of Shares or other shares of Preferred
Stock which is at such time convertible into the number of shares of Common
Stock which such Participant elects to sell; provided, however, that if the
prospective purchaser objects to the delivery of such Shares or other Preferred
Stock in lieu of Common Stock, such Participant shall convert such Shares or
Preferred Stock into Common Stock upon the closing of the sale contemplated
hereby and deliver Common Stock as provided in subparagraph 4.1(e)(i) above. 
The Company agrees to make any such conversion concurrent with the actual
transfer of such shares to the purchaser.
              (f)  The stock certificate or certificates that the Participant
delivers to the Selling Party pursuant to paragraph 4.1(e) shall be transferred
to the prospective purchaser in consummation of the sale of the Stock pursuant
to the terms and conditions specified in the Co-Sale Notice, and the Selling
Party shall concurrently therewith remit to such Participant that portion of the
sale proceeds to which such Participant is entitled by reason of its
participation in such sale.  To the extent that any prospective purchaser or
purchasers prohibits such assignment or otherwise refuses to purchase shares or
other securities from a Participant exercising its rights of co-sale hereunder,
the Selling Party shall not sell to such prospective purchaser or purchasers any
Stock unless and until, simultaneously with such sale, the Selling Party shall
purchase such shares or other securities from such Participant.
              (g)  The exercise or non-exercise of the rights of the
Participants hereunder to participate in one or more sales of Stock made by a
Selling Party shall not adversely affect their rights to participate in
subsequent sales of Stock subject to paragraph 4.1(a).
              (h)  Subject to the rights of the Purchasers who have elected to
participate in the sale of the Stock subject to the Co-Sale Notice, the Selling
Party may, not later than sixty (60) days following delivery to the Company and
each of the Purchasers of the Notice, conclude a transfer of any or all of the
Stock covered by the Notice on terms and conditions not materially more
favorable to the transferor than those described in the Notice.  Any proposed
transfer on terms and conditions materially more favorable than those described
in the Co-Sale Notice, as well as any subsequent proposed transfer of any of the
Stock by the Selling Party, shall again be subject to the co-sale rights of the
Purchasers and shall require compliance by the Selling Party with the procedures
described in this Section 4.
    b.        Termination of Right of Co-Sale.  Notwithstanding anything in 
         this Section 4 to the contrary, the right of co-sale shall terminate 
         upon (and shall not be applicable with respect to) the earlier of (i) 
         the closing of the Company's initial firm commitment underwritten 
         public offering pursuant to an effective registration statement under 
         the Securities Act, (ii) the closing of the Company's sale of all or 
         substantially all of its assets or the acquisition of the Company by 
         another entity by means of merger or consolidation resulting in the 
         exchange of the outstanding shares of the Company's capital stock for 
         securities or consideration issued, or caused to be issued, by the 
         acquiring entity or its subsidiary, or (iii) such time as the    
         Purchasers hold an aggregate of less than 1,000,000 (appropriately 
         adjusted for stock splits, dividends, recapitalizations and similar 
         events) Shares and Conversion Shares.
    c.        Exempt Transfers.
              (a)  Notwithstanding the foregoing, the co-sale rights of the
Purchasers shall not apply to any transfer to the ancestors, descendants or
spouse or to trusts for the benefit of such persons or the transferring
Stockholder or Purchaser or to any transfer by an Purchaser to a partner or
affiliate of such Purchaser, or a retired partner of such Purchaser who retires
after the date hereof; or to the estate of any such partner or retired partner
or the transfer by gift, will or intestate succession of any partner to such
partner's spouse or to the siblings, lineal descendants or ancestors of such
partner or such partner's spouse; provided that (A) the transferring Stockholder
or Purchaser shall inform the Purchasers or the Company (which shall then inform
the Purchasers) of such pledge, transfer or gift prior to effecting it and (B)
the pledgee, transferee or donee shall furnish the Purchasers with a written
agreement to be bound by and comply with all provisions of Section 4 of this
Agreement.  Such transferred Stock shall remain "Stock" hereunder, and such
pledgee, transferee shall be treated as a "Stockholder" or "Purchaser," as
applicable, for purposes of this Agreement.
              (b)  Notwithstanding the foregoing, the provisions of Section 4
shall not apply to the sale of any Stock (i) to the public pursuant to a
registration statement filed with, and declared effective by, the Commission
under the Securities Act or (ii) to the Company pursuant to the terms of the
Company's repurchase rights set forth in restricted stock purchase agreements
with the Stockholders or in connection with the termination of a Stockholder's
employment with the Company or (iii) if prior to such sale, the Stockholder held
less than one percent (1%) of the Company's outstanding shares.
              (c)  This Section 4 shall in no manner limit the right of the
Company to repurchase securities from Stockholders, consultants, employees or
directors pursuant to its repurchase rights and first refusal rights set forth
in applicable stock purchase agreements.
         4.4  Prohibited Transfers.  Notwithstanding the foregoing, any
attempt by a Stockholder or Purchaser to transfer Stock in violation of Section
4 hereof shall be void and the Company agrees it will not effect such a transfer
nor will it treat any alleged transferee as the holder of such shares without
the written consent of sixty percent (60%) of the outstanding shares of the
Company's Preferred Stock.
         4.5  Legend.
              (a)  Each certificate representing shares of Stock now or
hereafter owned by the Stockholders or Purchasers or issued to any person in
connection with a transfer pursuant to paragraph 4.3(a) hereof shall be endorsed
with the following legend:
         "THE SALE, PLEDGE, HYPOTHECATION OR TRANSFER OF THE
         SECURITIES REPRESENTED BY THIS CERTIFICATE IS SUBJECT TO THE
         TERMS AND CONDITIONS OF AN INVESTORS RIGHTS AGREEMENT, BY
         AND BETWEEN THE STOCKHOLDER, THE COMPANY AND CERTAIN HOLDERS
         OF STOCK OF THE COMPANY.  COPIES OF SUCH AGREEMENT MAY BE
         OBTAINED 
         UPON WRITTEN REQUEST TO THE SECRETARY OF THE COMPANY."
              (b)  Each Stockholder and Purchaser agrees that the Company may
instruct its transfer agent to impose transfer restrictions on the shares
represented by certificates bearing the legend referred to in paragraph 4.5(a)
above to enforce the provisions of this Section 4 and the Company agrees to
promptly do so.  The legend shall be removed upon termination of the provisions
of Section 4 of this Agreement.
         4.6  Assignability of Rights.  The co-sale rights granted to the
Purchasers hereunder shall be assignable only to an assignee or transferee who
acquires at least 75,000 shares of Preferred Stock or Common Stock issued upon
conversion thereof.
         4.7  Stock Split.  All references to numbers of shares in this
Section 4 shall be appropriately adjusted to reflect any stock dividend, split,
combination or other recapitalization of shares by the Company occurring after
the date of this Agreement.
5.       Amendments to Prior Agreements; Waivers.
    a.        Prior Investors Rights Agreement.  The Investors Rights Agreement
         dated March 18, 1996 (the "Prior Rights Agreement") is hereby    
         terminated and superseded in its entirety by this Agreement.  Holders 
         of outstanding Series A, Series B, Series C, Series D and Series E-1 
         Preferred Stock hereby consent to the foregoing as parties to the 
         Prior Rights Agreement.
    b.        Waivers.  The holders of the Series A, Series B, Series C, Series
         D and Series E-1  Preferred Stock hereby waive any rights they may 
         have pursuant to the Prior Rights Agreement to receive notice of the 
         issuance of or to purchase or otherwise acquire the Series E Preferred
         Stock being issued pursuant to the 1996 Series E Agreement (and the 
         Common Stock issuable upon conversion of such Series E Preferred 
         Stock).
6.       Miscellaneous.
    a.        Waivers and Amendments.  With the written consent of the Company 
         and the record holders of more than sixty percent (60%) of the Shares 
         and/or the Conversion Stock and, to the extent Stockholders are  
         specifically affected by a waiver, amendment or modification of  
         Section 4 hereof, by each such Stockholder, the obligations of the 
         Company and the rights of the holders of the Shares and the Conversion
         Stock under this Agreement may be waived (either generally or in a 
         particular instance, either retroactively or prospectively and either 
         for a specified period of time or indefinitely), and with the same 
         consent the Company, when authorized by resolution of its Board of 
         Directors, may enter into a supplementary agreement for the purpose of
         adding any provisions to or changing in any manner or eliminating any 
         of the provisions of this 
         Agreement; provided, however, that no such 
         waiver or supplemental agreement shall reduce the aforesaid percentage
         of the Shares and/or the Conversion Stock, the holders of which are 
         required to consent to any waiver or supplemental agreement without 
         the consent of the record holders of all of the Shares and/or the 
         Conversion Stock and any such waiver or supplementary agreement that 
         amends the proviso to the first sentence of the second paragraph of 
         Section 2.5(b) hereof , the proviso to the first sentence of Section 
         2.6(b) hereof or the proviso to Section 2.14 hereof or that otherwise 
         adversely affects any individual Holder only shall require the consent
         of such Holder.  Upon the effectuation of each such waiver, consent, 
         agreement, amendment or modification the Company shall promptly given 
         written notice thereof to the record holders of the Shares and/or the 
         Conversion Stock who have not previously consented thereto in writing. 
         Neither this Agreement nor any provisions hereof may be changed, 
         waived, discharged or terminated orally, but only by a signed    
         statement in writing.
    b.        Governing Law.  This Agreement shall be governed in all respects 
         by the laws of the State of California as such laws are applied to 
         agreements between California residents entered into and to be   
         performed entirely within California.
         
    c.        Successors and Assigns.  Except as otherwise expressly provided 
         herein, the provisions hereof shall inure to the benefit of, and be 
         binding upon, the successors, assigns, heirs, executors and      
         administrators of the parties hereto.
    d.        Entire Agreement.  This Agreement constitutes the full and entire
         understanding and agreement between the parties with regard to the 
         subjects hereof and thereof.
    e.        Notices.  All notices and other communications required or  
         permitted hereunder shall be effective upon receipt and shall be in 
         writing and may be delivered in person, by telecopy, electronic mail, 
         overnight delivery service or U.S. mail, in which event it may be 
         mailed by first-class, certified or registered, postage prepaid, 
         addressed (a) if to a Purchaser or Holder, at such address as such 
         Purchaser or Holder shall have furnished the Company in writing, or, 
         until any such holder so furnishes an address to the Company, then to 
         and at the address of the last holder of such securities who has so 
         furnished an address to the Company, or (b) if to the Company, at its 
         address set forth at the beginning of this Agreement, or at such other
         address as the Company shall have furnished to the Purchasers, Holders
         and each such other holder in writing.  Notwithstanding the foregoing,
         all notices and communications to addresses outside the United States 
         shall be given by telecopier and confirmed in writing sent by    
         overnight or two-day courier service.  
    f.        Titles and Subtitles.  The titles of the paragraphs and     
         subparagraphs of this Agreement are for convenience of reference only 
         and are not to be considered in construing this Agreement.
    g.        Counterparts.  This Agreement may be executed in any number of 
         counterparts, each of which shall be an original, but all of which 
         together shall constitute one instrument.
    h.        Nominees.  Securities registered in the name of a nominee for a 
         Purchaser or a Holder shall, for purposes of this Agreement, be  
         treated as being owned by such Purchaser or Holder. 
    The foregoing Investors Rights Agreement is hereby executed as of the date
first above written.
                             FOCAL, INC.
                             By:  
                                  ---------------------------------
                                  ▇▇▇▇▇ ▇▇▇▇▇▇▇, President
STOCKHOLDERS:
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▇▇▇▇▇ ▇▇▇▇                        ▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇
 
 HOLDERS:
     Name of Holder             
-------------------------------------
APA EXCELSIOR FUND IV, L.P. 
    By APA Excelsior IV Partners, L.P.,
    its General Partner
By:
    ---------------------------------
    ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇, General Partner
APA EXCELSIOR IV/OFFSHORE, L.P. 
    By  Patricof & Co. Ventures, Inc.,
    its Investment Adviser 
By:
    --------------------------------
    ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇, Vice President 
              
    
THE P/A FUND 
      By  APA Pennsylvania Partners II, L.P.,
      its General Partner 
By:
     ----------------------------------
     ▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇, General Partner 
    
WARBURG PINCUS EMERGING GROWTH FUND 
    
By:
     ---------------------------------
Title:
      --------------------------------
PACIFIC HORIZON VENTURES
By:
     ---------------------------------
Title:
      --------------------------------
GMGF, L.P. 
By:
     ---------------------------------
Title:
      --------------------------------
SENTRON MEDICAL, INC. 
By:
     ---------------------------------
Title:
      --------------------------------
--------------------------------------
▇▇▇ ▇▇▇▇▇▇▇▇▇▇
THE CIT GROUP/EQUITY INVESTMENTS, INC.
By:
     ---------------------------------
Title:
      --------------------------------
DELPHI INVESTMENTS II, L.P.
By:
     ---------------------------------
Title:
      --------------------------------
DELPHI VENTURES II, L.P.
By:
     ---------------------------------
Title:
      --------------------------------
DOMAIN PARTNERS II, L.P.
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇ ▇. ▇▇▇▇▇▇
--------------------------------------
Signature
▇▇▇▇▇▇▇  MANAGEMENT, L.L.C.
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇ & CO., L.P.
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇ HEALTHCARE INVESTMENTS, L.P.
By:
   ------------------------------------
Title:
      ---------------------------------
GENERAL ELECTRIC PENSION TRUST
By:
     ---------------------------------
Title:
      --------------------------------
GLENBROOK PARTNERS
By:
     ---------------------------------
Title:
      --------------------------------
H & Q HEALTHCARE INVESTORS
By:
     ---------------------------------
Title:
      --------------------------------
H & Q FOCAL INVESTORS, L.P. 
By:
     ---------------------------------
Title:
      --------------------------------
H & Q LIFE SCIENCES INVESTORS
By:
     ---------------------------------
Title:
      --------------------------------
HELIOS PARTNERS, L.P.
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇
---------------------------------------
Signature
INVEMED ASSOCIATES, INC.
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
--------------------------------------
Signature
KLEINER, PERKINS, CAULFIELD & ▇▇▇▇▇ VI
By:
     ---------------------------------
Title:
      --------------------------------
KPCB FOUNDERS' FUND
By:
     ---------------------------------
Title:
      --------------------------------
KPCB VI FOUNDERS' FUND
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇
--------------------------------------
Signature
▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇
--------------------------------------
Signature
▇▇▇▇▇▇▇▇ VI
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇▇ VII
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇▇ ASSOCIATES
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇▇ ASSOCIATES FUND II
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇▇ MEDICAL PARTNERS
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇▇ MEDICAL PARTNERS 1992
By:
     ---------------------------------
Title:
      --------------------------------
OLD COURT LIMITED
By:
     ---------------------------------
Title:
      --------------------------------
PARVEST U.S. PARTNERS II, C.V.
By:
     ---------------------------------
Title:
      --------------------------------
ROUSSO FAMILY TRUST
By:
     ---------------------------------
Title:
      --------------------------------
SINGAPORE BIO-INNOVATIONS PTE LTD
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇ ▇. Step
--------------------------------------
Signature
VULCAN VENTURES, INC.
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇ ▇. Widensohler
--------------------------------------
Signature
   
WARRANT HOLDERS:
COMDISCO, INC.
By:
     ---------------------------------
Title:
      --------------------------------
BANK OF BOSTON
By:
     ---------------------------------
Title:
      --------------------------------
▇▇▇▇▇▇▇ INVESTMENT SECURITIES, L.P.
By:
     ---------------------------------
Title:
      --------------------------------
MMC/GATX PARTNERSHIP NO.1
GATX CAPITAL CORPORATION
By:
     ---------------------------------
Title:
      --------------------------------