7,000,000 Shares Seattle Genetics, Inc. Common Stock UNDERWRITING AGREEMENT

Exhibit 1.1

7,000,000 Shares

Seattle Genetics, Inc.

Common Stock

UNDERWRITING AGREEMENT

February 4, 2004

CIBC World Markets Corp.

Banc of America Securities LLC

▇▇ ▇▇▇▇▇▇▇▇▇ + Co, LLC,

as Representatives of the several

Underwriters named in Schedule I hereto

c/o CIBC World Markets Corp.

▇▇▇ ▇^▇▇ ▇▇▇▇▇▇, ▇^▇▇ ▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Ladies and Gentlemen:

Seattle Genetics, Inc., a Delaware corporation (the “Company”) proposes, subject to the terms and conditions contained herein, to sell to you and the other underwriters named on Schedule I to this Agreement (the “Underwriters”), for whom you are acting as Representatives (the “Representatives”), an aggregate of 7,000,000 shares (the “Firm Shares”) of the Company’s common stock, $0.001 par value per share (the “Common Stock”). The respective amounts of the Firm Shares to be purchased by each of the several Underwriters are set forth opposite their names on Schedule I hereto. In addition, the Company proposes to grant to the Underwriters an option to purchase up to an additional 1,050,000 shares (the “Option Shares”) of Common Stock from the Company. The Firm Shares and the Option Shares are collectively called the “Shares.”

The Company has prepared and filed in conformity with the requirements of the Securities Act of 1933, as amended (the “Securities Act”), and the published rules and regulations thereunder (the “Rules”) adopted by the Securities and Exchange Commission (the “Commission”) a Registration Statement (as hereinafter defined) on Form S-3 (No. 333-111269), which was declared effective on January 12, 2004, relating to the Shares and the offering thereof from time to time in accordance with Rule 415 under the Securities Act. Copies of such Registration Statement (including all amendments thereof) and of the related Preliminary Prospectus (as hereinafter defined) have heretofore been delivered by the Company to you. The term “Preliminary Prospectus” means any preliminary prospectus, including the documents incorporated by reference therein and any supplement or amendment to such preliminary prospectus used in connection with the offer of Shares prior to the date hereof. The term “Registration Statement” as used in this Agreement means the initial registration statement (including all exhibits, financial schedules and all documents and information deemed to be a

part of the Registration Statement through incorporation by reference or otherwise), as amended at the time and on the date it becomes effective (the “Effective Date”), including the information (if any) contained in the form of final prospectus filed with the Commission pursuant to Rule 424(b) of the Rules and deemed to be part thereof at the time of effectiveness pursuant to Rule 430A of the Rules. If the Company has filed an abbreviated registration statement to register additional Shares pursuant to Rule 462(b) under the Rules (the “462(b) Registration Statement”), then any reference herein to the Registration Statement shall also be deemed to include such 462(b) Registration Statement. The term “Prospectus” as used in this Agreement means the prospectus in the form included in the Registration Statement at the time of effectiveness and any prospectus filed with the Commission pursuant to Rule 424(b) of the Rules. Reference made herein to any Preliminary Prospectus or to the Prospectus shall be deemed to refer to and include any documents incorporated by reference therein pursuant to Item 12 of Form S-3 under the Securities Act, as of the date of such Preliminary Prospectus or the Prospectus, as the case may be, and any reference to any amendment or supplement to any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include any document filed under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), after the date of such Preliminary Prospectus or the Prospectus, as the case may be, and incorporated by reference in such Preliminary Prospectus or the Prospectus, as the case may be.

The Company has caused to be delivered to you copies of the Preliminary Prospectus and has consented to the use of such copies for the purposes permitted by the Securities Act.

The Company understands that the Underwriters propose to make a public offering of the Shares, as set forth in and pursuant to the Prospectus, as soon after the date of this Agreement as the Representatives deem advisable. The Company hereby confirms that the Underwriters and dealers have been authorized to distribute or cause to be distributed each Preliminary Prospectus and are authorized to distribute the Prospectus (as from time to time amended or supplemented if the Company furnishes amendments or supplements thereto to the Underwriters).

1. Sale, Purchase, Delivery and Payment for the Shares. On the basis of the representations, warranties and agreements contained in, and subject to the terms and conditions of, this Agreement:

(a) The Company agrees to issue and sell to each of the Underwriters, and each of the Underwriters agrees, severally and not jointly, to purchase from the Company, at a purchase price of $7.755 per share (the “Initial Price”), the number of Firm Shares set forth opposite the name of such Underwriter under the column “Number of Firm Shares to be Purchased from the Company” on Schedule I to this Agreement, subject to adjustment in accordance with Section 6 hereof.

(b) The Company hereby grants to the several Underwriters an option to purchase, severally and not jointly, all or any part of the Option Shares at the Initial Price. The number of Option Shares to be purchased by each Underwriter shall be the same percentage (adjusted by the Representatives to eliminate fractions) of the total number of Option Shares to be purchased by the Underwriters as such Underwriter is purchasing of

the Firm Shares. Such option may be exercised only to cover over-allotments in the sales of the Firm Shares by the Underwriters and may be exercised in whole or in part at any time on or before 12:00 noon, New York City time, on the business day before the Firm Shares Closing Date (as defined below), and from time to time thereafter within 30 days after the date of this Agreement, in each case upon written, facsimile or telegraphic notice, by the Representatives to the Company no later than 12:00 noon, New York City time, on the business day before the Firm Shares Closing Date (if exercised prior to the Firm Shares Closing Date as provided above) or at least two business days before the Option Shares Closing Date (as defined below), as the case may be, setting forth the number of Option Shares to be purchased and the time and date (if other than the Firm Shares Closing Date) of such purchase.

(c) Payment of the purchase price for, and delivery of certificates for, the Firm Shares shall be made at the offices of CIBC World Markets Corp., ▇▇▇ ▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇, at 10:00 a.m., New York City time, on the third business day following the date of this Agreement or at such time on such other date, not later than ten (10) business days after the date of this Agreement, as shall be agreed upon by the Company and the Representatives (such time and date of delivery and payment are called the “Firm Shares Closing Date”). In addition, in the event that any or all of the Option Shares are purchased by the Underwriters, payment of the purchase price, and delivery of the certificates, for such Option Shares shall be made at the above-mentioned offices, or at such other place as shall be agreed upon by the Representatives and the Company, on each date of delivery as specified in the notice from the Representatives to the Company (such time and date of delivery and payment are called the “Option Shares Closing Date”). The Firm Shares Closing Date and any Option Shares Closing Date are called, individually, a “Closing Date” and, together, the “Closing Dates.”

(d) Payment shall be made to the Company by wire transfer of immediately available funds or by certified or official bank check or checks payable in New York Clearing House (same day) funds drawn to the order of the Company, against delivery of the Shares to the Representatives for the respective accounts of the Underwriters of the Shares to be purchased by them.

(e) The Shares shall be delivered by or on behalf of the Company to the Representatives through the facilities of the Depository Trust Company (“DTC”) for the account of each such Underwriter unless the Underwriters direct otherwise.

2. Representations and Warranties of the Company. The Company represents and warrants to each Underwriter as of the date hereof, as of the Firm Shares Closing Date and as of each Option Shares Closing Date (if any), as follows:

(a) On the Effective Date, the Registration Statement complied, and on the date of the Prospectus, the date any post-effective amendment to the Registration Statement becomes effective, the date any supplement or amendment to the Prospectus is filed with the Commission and each Closing Date, the Registration Statement and the Prospectus (and any amendment thereof or supplement thereto) will comply, in all

material respects, with the requirements of the Securities Act and the Rules and the Exchange Act and the rules and regulations of the Commission thereunder. The Registration Statement did not, as of the Effective Date, contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary in order to make the statements therein not misleading; and on the Effective Date and the other dates referred to above neither the Registration Statement nor the Prospectus, nor any amendment thereof or supplement thereto, will contain any untrue statement of a material fact or will omit to state any material fact required to be stated therein or necessary in order to make the statements therein not misleading. When any related preliminary prospectus was first filed with the Commission (whether filed as part of the Registration Statement or any amendment thereto) and when any amendment thereof or supplement thereto was first filed with the Commission, such preliminary prospectus as amended or supplemented complied in all material respects with the applicable provisions of the Securities Act and the Rules and did not contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary in order to make the statements therein not misleading, other than information permitted to be omitted pursuant to Rule 430A. If applicable, each Preliminary Prospectus and the Prospectus delivered to the Underwriters for use in connection with this offering was identical to the electronically transmitted copies thereof filed with the Commission pursuant to ▇▇▇▇▇, except to the extent permitted by Regulation S-T. Notwithstanding the foregoing, none of the representations and warranties in this paragraph 4(a) shall apply to statements in, or omissions from, the Registration Statement or the Prospectus made in reliance upon, and in conformity with, information herein or otherwise furnished in writing by the Representatives on behalf of the several Underwriters for use in the Registration Statement or the Prospectus. With respect to the preceding sentence, the Company acknowledges that the only information furnished in writing by the Representatives on behalf of the several Underwriters for use in the Registration Statement or the Prospectus in paragraphs 3, 10, 11, 12, 13, 14, 15 and 16 under the caption “Underwriting” in the Prospectus.

(b) The Registration Statement is effective under the Securities Act and no stop order preventing or suspending the effectiveness of the Registration Statement or suspending or preventing the use of the Prospectus has been issued by the Commission and no proceedings for that purpose have been instituted or are threatened under the Securities Act. Any required filing of the Prospectus and any supplement thereto pursuant to Rule 424(b) of the Rules has been or will be made in the manner and within the time period required by such Rule 424(b).

(c) The documents incorporated by reference in the Registration Statement and the Prospectus, at the time they became effective or were filed with the Commission, as the case may be, complied in all material respects with the requirements of the Securities Act or the Exchange Act, as applicable, and the rules and regulations of the Commission thereunder, and none of such documents contained an untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading, and any further documents so filed and incorporated by reference in the Registration Statement and the Prospectus, when such documents

become effective or are filed with the Commission, as the case may be, will conform in all material respects to the requirements of the Securities Act or the Exchange Act, as applicable, and the rules and regulations of the Commission thereunder and will not contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they are made, not misleading; provided, however, that this representation and warranty shall not apply to any statements or omissions made in reliance upon and in conformity with information furnished in writing to the Company by an Underwriter through the Representatives expressly for use therein.

(d) The financial statements of the Company (including all notes and schedules thereto) included or incorporated by reference in the Registration Statement and the Prospectus present fairly the financial position of the Company as of the dates indicated and the results of its operations, stockholder’ equity and changes in their cash flows for the periods specified; said financial statements and related schedules and notes thereto, and the unaudited financial information filed with the Commission as part of the Registration Statement, have been prepared in conformity with generally accepted accounting principles, consistently applied throughout the periods involved, and the supporting schedules included in the Registration Statement present fairly the information required to be stated therein; and the pro forma financial information, and the related notes thereto, included in the Registration Statement and the Prospectus has been prepared in accordance with the applicable requirements of the Securities Act and the Exchange Act, as applicable, and is based upon good faith estimates and assumptions believed by the Company to be reasonable.

(e) There has not occurred any material adverse change, or any development involving a prospective material adverse change, in the condition, financial or otherwise, or in the earnings, business, operations or prospects of the Company, from that set forth in the Prospectus (exclusive of any amendments or supplements thereto subsequent to the date of this Agreement).

(f) PricewaterhouseCoopers LLP who have certified certain financial statements of the Company, are independent public accountants as required by the Securities Act.

(g) The Company is duly incorporated and is validly existing as a corporation in good standing under the laws of the State of Delaware, with power and authority (corporate and other) to own its properties and conduct its business as described in the Registration Statement and the Prospectus, and has been duly qualified as a foreign corporation for the transaction of business and is in good standing or, where applicable, validly existing under the laws of each other jurisdiction in which it owns or leases properties, or conducts any business, so as to require such qualification, other than where the failure to be so qualified, in good standing or validly existing would not have a material adverse effect on the general affairs, business, prospects, management, financial position, stockholders’ equity or results of operations of the Company, (a “Material Adverse Effect”).

(h) The Company has all requisite corporate power and authority, and all necessary authorizations, approvals, consents, orders, licenses, certificates and permits of and from all governmental or regulatory bodies or any other person or entity (collectively, the “Permits”), to own, lease and license its assets and properties and conduct its business, all of which are valid and in full force and effect, except where the lack of such Permits, individually or in the aggregate, would not have a Material Adverse Effect. The Company has fulfilled and performed in all material respects all of its material obligations with respect to such Permits and no event has occurred that allows, or after notice or lapse of time would allow, revocation or termination thereof or results in any other material impairment of the rights of the Company thereunder. Except as may be required under the Securities Act and state and foreign Blue Sky laws, no other Permits are required to enter into, deliver and perform this Agreement and to issue and sell the Shares. All of the descriptions in the Registration Statement and the Prospectus of the legal and governmental procedures and requirements of the United States Food and Drug Administration (the “FDA”) or any foreign, state or local governmental body exercising comparable authority are accurate in all material respects.

(i) Except as described in the Registration Statement and the Prospectus, the Company owns, is licensed to use or otherwise possesses adequate rights to use the patents, patent rights, licenses, inventions, trademarks, service marks, trade names, copyrights and know-how, including trade secrets and other unpatented and/or unpatentable proprietary or confidential information, systems, processes or procedures (collectively, the “Intangibles”), reasonably necessary to carry on the business conducted by it, except to the extent that the failure to own, be licensed to use or otherwise possess adequate rights to use such Intangibles would not, individually or in the aggregate, reasonably be expected to have a Material Adverse Effect; the Company has not received any notice of infringement of or conflict with, and the Company has no knowledge of any infringement of or conflict with, asserted rights of others with respect to its Intangibles which would, individually or in the aggregate, reasonably be expected to result in a Material Adverse Effect; the discoveries, inventions, products or processes of the Company referred to in the Registration Statement and the Prospectus do not, to the knowledge of the Company, infringe or conflict with any right or patent of any third party, or any discovery, invention, product or process which is the subject of a patent application filed by any third party which patent application has been published or is otherwise known to the Company which could, individually or in the aggregate, reasonably be expected to result in a Material Adverse Effect; except as set forth in the Registration Statement and the Prospectus, the Company is not obligated to pay a royalty, grant a license or provide other consideration to any third party in connection with its patents, patent rights, licenses, inventions, trademarks, service marks, trade names, copyrights and know-how which could, individually or in the aggregate, reasonably be expected to have a Material Adverse Effect; and no third party, including any academic or governmental organization, possesses rights to the Intangibles which, if exercised, could reasonably be expected to have a Material Adverse Effect.

(j) The Company has good and marketable title in fee simple to all items of real property and good and marketable title to all personal property owned by it, in each case free and clear of all liens, encumbrances, claims, security interests and defects

except such as are described or referred to in the Registration Statement and the Prospectus or such as do not materially affect the value of such property and do not interfere with the use made or proposed to be made of such property by the Company; and any real property and buildings held under lease by the Company are held by them under valid, existing and enforceable leases with such exceptions as are not material and do not interfere with the use made or proposed to be made of such property and buildings by the Company.

(k) Other than as set forth in the Registration Statement and the Prospectus, there are no legal or governmental investigations, actions, suits or proceedings pending or, to the knowledge of the Company, threatened against or affecting the Company or any of its properties or to which the Company is or may be a party or to which any property of the Company is or may be the subject which, if determined adversely to the Company, could, individually or in the aggregate, have, or reasonably be expected to have, a Material Adverse Effect, and, to the Company’s knowledge, no such proceedings are threatened or contemplated by governmental authorities or threatened by others.

(l) There are no statutes, regulations or legal or governmental investigations, actions, suits or proceedings pending or, to the knowledge of the Company, threatened that are required to be described in the Registration Statement or Prospectus or to be filed as exhibits to the Registration Statement, as the case may be, that are not described or filed as required

(m) Since the respective dates as of which information is given in the Registration Statement and the Prospectus, the studies, tests and preclinical and clinical trials conducted by or on behalf of the Company that are described in the Registration Statement and the Prospectus were and, if still pending, are being conducted in accordance with experimental protocols, procedures and controls pursuant to, where applicable, accepted professional scientific standards; the descriptions of the results of such studies, tests and trials contained in the Registration Statement and the Prospectus are accurate and complete summaries of such studies, tests and trials and do not omit any material facts necessary to make the statements therein not misleading; and the Company has not received any notices or correspondence from the FDA or any foreign, state or local governmental body exercising comparable authority requiring the termination, suspension or material modification of any studies, tests or preclinical or clinical trials conducted by or on behalf of the Company which termination, suspension or material modification would reasonably be expected to have a Material Adverse Effect.

(n) There is no document, contract or other agreement required to be described in the Registration Statement or Prospectus or to be filed as an exhibit to the Registration Statement which is not described or filed as required by the Securities Act or Rules. Each description of a contract, document or other agreement in the Registration Statement and the Prospectus accurately reflects in all material respects the terms of the underlying contract, document or other agreement. Each contract, document or other agreement described in the Registration Statement and Prospectus or listed in the Exhibits to the Registration Statement or incorporated by reference is in full force and effect and is valid and enforceable by and against the Company in accordance with its terms, other

than agreements which have by their terms expired or which the Company has terminated after determining that terminating such agreements would not have a Material Adverse Effect. Neither the Company nor to the Company’s knowledge, any other party is in default in the observance or performance of any term or obligation to be performed by it under any such agreement, and no event has occurred which with notice or lapse of time or both would constitute such a default, in any such case which default or event, individually or in the aggregate, would have a Material Adverse Effect. No default exists, and no event has occurred which with notice or lapse of time or both would constitute a default, in the due performance and observance of any term, covenant or condition, by the Company of any other agreement or instrument to which the Company is a party or by which Company or its properties or business may be bound or affected which default or event, individually or in the aggregate, would have a Material Adverse Effect.

(o) The Company is not, and with the giving of notice or lapse of time or both would not be, in violation of or in default under its certificate of incorporation or by-laws or any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Company is a party or by which it or any of its properties is bound, except for violations and defaults which would not, individually or in the aggregate, have a Material Adverse Effect.

(p) This Agreement has been duly authorized, executed and delivered by the Company.

(q) The issuance and sale of the Shares and the performance by the Company of its obligations under this Agreement and the consummation of the transactions contemplated herein and in the Prospectus will not conflict with, result in a breach of or violate any of the terms or provisions of, or constitute a default under, any indenture, mortgage, deed of trust, loan agreement or other material agreement or instrument to which the Company is a party or by which the Company is bound or to which any of the property or assets of the Company is subject, nor will any such action result in any violation of the provisions of the certificate of incorporation or by-laws of the Company or any applicable law or statute or any order, rule or regulation of any court or governmental agency or body having jurisdiction over the Company or any of its respective properties; and no consent, approval, authorization, order, license, registration or qualification of or with any such court or governmental agency or body is required for the issuance and sale of the Shares or the consummation by the Company of the transactions contemplated by this Agreement and the Prospectus, except such consents, approvals, authorizations, orders, licenses, registrations or qualifications as have been obtained or made under the Securities Act and as may be required under state securities or blue sky laws in connection with the purchase and distribution of the Shares by the Underwriters.

(r) The Company has authorized and outstanding capital stock as set forth under the caption “Capitalization” in the Prospectus as of the dates set forth therein and such authorized capital stock conforms as to legal matters to the description thereof set forth in the Registration Statement and the Prospectus, and all of the outstanding shares

of capital stock of the Company have been duly authorized and validly issued, are fully paid and non-assessable and are not subject to any pre-emptive or similar rights; and, except as described in or expressly contemplated by the Registration Statement and the Prospectus, as of the dates set forth therein, there are no outstanding rights (including, without limitation, pre-emptive rights), warrants or options to acquire, or instruments convertible into or exchangeable for, any shares of capital stock or other equity interest in the Company, or any contract, commitment, agreement, understanding or arrangement of any kind relating to the issuance of any capital stock of the Company, any such convertible or exchangeable securities or any such rights, warrants or options; the Company has no subsidiaries and does not own any shares of capital stock or other equity interests or any instruments convertible into or exchangeable for, any shares of capital stock or other equity interest, or any contract, commitment, agreement, understanding or arrangement of any kind relating to the issuance of any capital stock, any such convertible or exchangeable securities or any such rights, warrants or options of any third party, except for such shares of capital stock purchased pursuant to the Company’s routine investment program and the Company’s right to repurchase at cost certain shares subject to vesting that were acquired by holders upon exercise of stock options.

(s) Each director and executive officer of the Company and each stockholder of the Company listed on Schedule II has delivered to the Representatives his written lock-up agreement substantially in the form attached to this Agreement as Exhibit A hereto (the “Lock-Up Agreement”) or in such other form as agreed with Representatives.

(t) All necessary corporate action has been duly and validly taken by the Company and to authorize the execution, delivery and performance of this Agreement and the issuance and sale of the Shares by the Company. This Agreement has been duly and validly authorized, executed and delivered by the Company and constitute and will constitute the legal, valid and binding obligation of the Company enforceable against the Company in accordance with its terms, except as the enforceability thereof may be limited by bankruptcy, insolvency, reorganization, moratorium or other similar laws affecting the enforcement of creditors’ rights generally and by general equitable principles.

(u) There are no existing or, to the knowledge of the Company, threatened labor disputes with the employees of the Company which would reasonably be expected to have a Material Adverse Effect.

(v) No relationship, direct or indirect, exists between or among the Company, on the one hand, and the directors, officers, stockholders, customers or suppliers of the Company, on the other hand, which is required by the Securities Act to be described in the Registration Statement and the Prospectus which is not so described.

(w) the Company has not taken nor will it take, directly or indirectly, any action designed to, or which might be reasonably expected to, cause or result in, or which has constituted or which might reasonably be expected to constitute, the stabilization or manipulation of the price of the Common Stock or any security of the Company to facilitate the sale or resale of any of the Shares.

(x) The statistical and market-related data included in the Registration Statement and the Prospectus are based on or derived from sources which are believed by the Company to be reliable.

(y) The Company has filed all Federal, state, local and foreign tax returns which are required to be filed through the date hereof, which returns are true and correct in all material respects or has received timely extensions thereof, and has paid all taxes shown on such returns and all assessments received by it to the extent that the same are material and have become due. There are no tax audits or investigations pending, which if adversely determined would have a Material Adverse Effect; nor are there any material proposed additional tax assessments against the Company.

(z) The Shares have been duly authorized for quotation on the National Association of Securities Dealers Automated Quotation (“Nasdaq”) National Market System. The Shares have been duly authorized, and, when issued and delivered to and paid for by the Underwriters in accordance with the terms of this Agreement, will be duly issued and will be fully paid and non-assessable and will conform to the description thereof set forth in the Registration Statement and the Prospectus; and the issuance of the Shares is not subject to any preemptive or similar rights.

(aa) The Company has taken no action designed to, or likely to have the effect of, terminating the registration of the Common Stock under the Exchange Act or the quotation of the Common Stock on the Nasdaq National Market, nor has the Company received any notification that the Commission or the Nasdaq National Market is contemplating terminating such registration or quotation.

(bb) The books, records and accounts of the Company accurately and fairly reflect, in reasonable detail, the transactions in, and dispositions of, the assets of, and the results of operations of, the Company. The Company maintains a system of internal accounting controls sufficient to provide reasonable assurances that (i) transactions are executed in accordance with management’s general or specific authorizations, (ii) transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles and to maintain asset accountability, (iii) access to assets is permitted only in accordance with management’s general or specific authorization and (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences; the chief executive officer and the chief financial officer of the Company have made all certifications required by the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act of 2002 (the “▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act”) and any related rules and regulations promulgated by the Commission, and the statements contained in any such certification are complete and correct; the Company is otherwise in compliance in all material respects with all applicable effective provisions of the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act and is actively taking steps to ensure that it will be in compliance with other applicable provisions of the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act upon the effectiveness of such provisions.

(cc) The Company carries, or is covered by, insurance in such amounts and covering such risks as is adequate for the conduct of its business and the value of its properties and as is customary for companies engaged in similar businesses in similar industries.

(dd) The Company has established and maintains “disclosure controls and procedures” (as such term is defined in Rule 13a-14 under the Exchange Act, which (i) are designed to ensure that material information relating to the Company is made known to the Company’s principal executive officer and its principal financial officer by others within those entities, particularly during the periods in which the periodic reports required under the Exchange Act are being prepared; and (ii) provide for the periodic evaluation of the effectiveness of such disclosure controls and procedures as of the end of the period covered by the Company’s most recent annual or quarterly report filed with the Commission.

(ee) Based on the evaluation of its disclosure controls and procedures, the Company is not aware of (i) any significant deficiency in the design or operation of internal controls which could adversely affect the Company’s ability to record, process, summarize and report financial data or any material weaknesses in internal controls; or (ii) any fraud, whether or not material, that involves management or other employees who have a significant role in the Company’s internal controls.

(ff) Since the date of the most recent evaluation of such disclosure controls and procedures, there have been no changes that have materially affected, or are reasonably likely to materially affect, the Company’s internal control over financial reporting, including any corrective actions with regard to significant deficiencies and material weaknesses.

(gg) Except as described in the Prospectus, there are no material off-balance sheet arrangements (as defined in Item 303 of Regulation S-K), or any other relationships with unconsolidated entities or other persons, that may have a material current or future effect on the Company’s financial condition, revenues or expenses, changes in financial condition, results of operations, liquidity, capital expenditures or capital resources.

(hh) Since May 6, 2003 (i) all audit and non-audit services performed by PricewaterhouseCoopers LLP have been preapproved in accordance with the requirements set forth in Section 10A of the Exchange Act and (ii) PricewaterhouseCoopers LLP has not engaged and as of the date hereof is not engaging in any “prohibited activities” (as defined in Section 10A of the Exchange Act) on behalf of the Company.

(ii) The Company’s Board of Directors has validly appointed an audit committee whose composition satisfies the requirements of Rule 4350(d)(2) of the Rules of the National Association of Securities Dealers, Inc. (the “NASD Rules”) and the Board of Directors and/or the audit committee has adopted a charter that satisfies the requirements of Rule 4350(d)(1) of the NASD Rules. The audit committee has reviewed the adequacy of its charter since January 1, 2003. Neither the Board of Directors nor the audit committee has been informed of (1) any significant deficiencies in the design or operation of the Company’s internal controls which could adversely affect the

Company’s ability to record, process, summarize and report financial data or any material weakness in the Company’s internal controls; or (2) any fraud, whether or not material, that involves management or other employees of the Company who have a significant role in the Company’s internal controls.

(jj) Each approval, consent, order, authorization, designation, declaration or filing of, by or with any regulatory, administrative or other governmental body necessary in connection with the execution and delivery by the Company of this Agreement and the consummation of the transactions herein contemplated required to be obtained or performed by the Company (except such additional steps as may be required by the National Association of Securities Dealers, Inc. (the “NASD”) or may be necessary to qualify the Shares for public offering by the Underwriters under the state securities or Blue Sky laws) has been obtained or made and is in full force and effect.

(kk) There are no affiliations with the NASD among the Company’s officers, directors or, to the best of the knowledge of the Company, any five percent or greater stockholder of the Company, except as set forth in the Registration Statement or otherwise disclosed in writing to the Representatives.

(ll) The Company (i) is in compliance with any and all applicable foreign, federal, state and local laws and regulations relating to the protection of human health and safety, the environment or hazardous or toxic substances or wastes, pollutants or contaminants (collectively, “Environmental Laws”), (ii) has received all permits, licenses or other approvals required of it under applicable Environmental Laws to conduct its businesses and (iii) is in compliance with all terms and conditions of any such permit, license or approval, except where such noncompliance with Environmental Laws, failure to receive required permits, licenses or other approvals or failure to comply with the terms and conditions of such permits, licenses or approvals would not, individually or in the aggregate, reasonably be expected to have a Material Adverse Effect.

(mm) The Company is not and, after giving effect to the offering and the sale of the Shares and the application of the proceeds thereof, will not be an “investment company” or an entity “controlled” by and “investment company” as such terms are defined in the Investment Company Act of 1940, as amended (the “Investment Company Act”).

(nn) Neither the Company, its directors, officers or employees nor, to the Company’s knowledge, any other person associated with or acting on behalf of the Company has directly or indirectly, while acting on behalf of the Company (i) used any corporate funds for unlawful contributions, gifts, entertainment or other unlawful expenses relating to political activity; (ii) made any unlawful payment to foreign or domestic government officials or employees or to foreign or domestic political parties or campaigns from corporate funds; (iii) violated any provision of the Foreign Corrupt Practices Act of 1977, as amended; or (iv) made any other unlawful payment.

(oo) Except as described in the Prospectus or in the documents incorporated by reference into the Prospectus, the Company has not sold or issued any shares of Common

Stock during the six-month period preceding the date of the Prospectus, including any sales pursuant to Rule 144A under, or Regulations D or S of, the Securities Act, other than shares issued pursuant to employee benefit plans, qualified stock options plans or other employee compensation plans or pursuant to outstanding options, rights or warrants.

(pp) Each employee benefit plan, within the meaning of Section 3(3) of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”), that is maintained, administered or contributed to by the Company or any of its affiliates for employees or former employees of the Company and its affiliates has been maintained in material compliance with its terms and the requirements of any applicable statutes, orders, rules and regulations, including but not limited to ERISA and the Internal Revenue Code of 1986, as amended (“Code”); no prohibited transaction, within the meaning of Section 406 of ERISA or Section 4975 of the Code, has occurred with respect to any such plan excluding transactions effected pursuant to a statutory or administrative exemption; for each such plan which is subject to the funding rules of Section 412 of the Code or Section 302 of ERISA, no “accumulated funding deficiency,” as defined in Section 412 of the Code, has been incurred, whether or not waived, and the fair market value of the assets of each such plan (excluding for these purposes accrued but unpaid contributions) exceed the present value of all benefits accrued under such plan determined using reasonable actuarial assumptions.

(qq) Each of the Company, its directors and officers has not distributed and will not distribute prior to the later of (i) the Firm Shares Closing Date, or the Option Shares Closing Date, and (ii) completion of the distribution of the Shares, any offering material in connection with the offering and sale of the Shares other than any Preliminary Prospectus, the Prospectus, the Registration Statement and other materials, if any, permitted by the Securities Act.

(rr) No person has the right to require the Company to register any securities for offering and sale under the Securities Act by reason of the filing of the Registration Statement with the Commission or by reason of the issuance and sale of the Shares, except for rights which have been waived.

3. Conditions of the Underwriters’ Obligations. The obligations of the Underwriters under this Agreement are several and not joint. The respective obligations of the Underwriters to purchase the Shares are subject to each of the following terms and conditions:

(a) Notification that the Registration Statement has become effective shall have been received by the Representatives and the Prospectus shall have been timely filed with the Commission in accordance with Section 4(a) of this Agreement.

(b) No order preventing or suspending the use of any preliminary prospectus or the Prospectus shall have been or shall be in effect and no order suspending the effectiveness of the Registration Statement shall be in effect and no proceedings for such purpose shall be pending before or threatened by the Commission, and any requests for additional information on the part of the Commission (to be included in the Registration

Statement or the Prospectus or otherwise) shall have been complied with to the satisfaction of the Commission and the Representatives. If the Company has elected to rely upon Rule 430A, Rule 430A information previously omitted from the effective Registration Statement pursuant to Rule 430A shall have been transmitted to the Commission for filing pursuant to Rule 424(b) within the prescribed time period and the Company shall have provided evidence satisfactory to the Underwriters of such timely filing, or a post-effective amendment providing such information shall have been promptly filed and declared effective in accordance with the requirements of Rule 430A.

(c) The representations and warranties of the Company contained in this Agreement and in the certificates delivered pursuant to Section 3(d) shall be true and correct when made and on and as of each Closing Date as if made on such date. The Company shall have performed all covenants and agreements and satisfied all the conditions contained in this Agreement required to be performed or satisfied by them at or before such Closing Date.

(d) The Representatives shall have received on each Closing Date a certificate, addressed to the Representatives and dated such Closing Date, of the chief executive officer and the chief financial officer of the Company to the effect that: (i) the representations, warranties and agreements of the Company in this Agreement were true and correct when made and are true and correct as of such Closing Date; (ii) the Company has performed all covenants and agreements and satisfied all conditions contained herein; (iii) they have carefully examined the Registration Statement and the Prospectus and, in their opinion (A) as of the Effective Date, the Registration Statement and Prospectus did not include any untrue statement of a material fact and did not omit to state a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading, and (B) since the Effective Date no event has occurred which should have been set forth in a supplement or otherwise required an amendment to the Registration Statement or the Prospectus; and (iv) no stop order suspending the effectiveness of the Registration Statement has been issued and, to their knowledge, no proceedings for that purpose have been instituted or are pending under the Securities Act.

(e) The Representatives shall have received, at the time this Agreement is executed and on each Closing Date a signed letter from PricewaterhouseCoopers LLP addressed to the Representatives and dated, respectively, the date of this Agreement and each such Closing Date, in form and substance reasonably satisfactory to the Representatives containing statements and information of the type ordinarily included in accountants’ “comfort letters” to underwriters with respect to the financial statements and certain financial information contained in the Registration Statement and the Prospectus.

(f) The Representatives shall have received on each Closing Date from ▇▇▇▇▇▇ ▇▇▇▇▇▇ White & ▇▇▇▇▇▇▇▇▇ LLP, Seattle, Washington, counsel for the Company, an opinion, addressed to the Representatives and dated such Closing Date, and stating in effect that:

(i) The Company has been duly incorporated and is in good standing as a corporation under the laws of the State of Delaware, with full corporate power and authority to own or lease, as the case may be, and to operate its properties and conduct its business as described in the Prospectus; the Company is duly authorized to transact business in the corporate form as a foreign corporation under the laws of the State of Washington;

(ii) The Company’s authorized equity capitalization is as set forth in the Prospectus; the capital stock of the Company conforms in all material respects to the description thereof contained in the Final Prospectus; the Shares have been duly and validly authorized, and, when issued and delivered to and paid for by the Underwriters pursuant to the Underwriting Agreement, will be fully paid and nonassessable; the Shares are duly listed, and admitted and authorized for trading, subject to official notice of issuance, on the Nasdaq National Market; the Form Certificate is in valid and sufficient form; the holders of outstanding shares of capital stock of the Company are not entitled to preemptive or other rights to subscribe for the Shares under the Delaware General Corporation Law or the Certificate of Incorporation or Bylaws, or, to such counsel’s knowledge, any other agreement to which the Company is a party; and, except as set forth in the Prospectus, to such counsel’s knowledge, no options, warrants or other rights to purchase, agreements or other obligations to issue, or rights to convert any obligations into or exchange any Shares for, shares of capital stock of or ownership interests in the Company are outstanding;

(iii) To such counsel’s knowledge, there is no pending or threatened action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Company or its property of a character required to be disclosed in the Registration Statement that is not disclosed in the Prospectus, and, to such counsel’s knowledge, there is no franchise, contract or other document of a character required to be described in the Registration Statement or Prospectus, or to be filed as an exhibit thereto, which is not described or filed as required; and the statements included or incorporated by reference in the Prospectus under the headings “Description of Capital Stock,” “Management—Board Composition” and in the Registration Statement in Part II – Item 15 insofar as such statements summarize legal matters, agreements, documents or proceedings discussed therein, fairly represent the information called for with respect to such legal matters, agreements, documents or proceedings and fairly summarize the matters referred to therein;

(iv) The Registration Statement has become effective under the Securities Act; any required filing of the Prospectus, any Preliminary Prospectus and the Prospectus, and any supplements thereto, pursuant to Rule 424(b) has been made in the manner and within the time period required by Rule 424(b); to such counsel’s knowledge, no stop order suspending the effectiveness of the Registration Statement has been issued, no proceedings for that purpose have been instituted or threatened; the Registration Statement and the Prospectus (other than the financial statements and other financial and statistical information

contained therein, as to which such counsel need not express an opinion) comply as to form in all material respects with the applicable requirements of the Securities Act and the rules thereunder; each document filed pursuant to the Exchange Act and incorporated by reference in the Registration Statement and the Prospectus (other than the financial statements and other financial and statistical information contained therein, as to which such counsel need not express an opinion) complied as to form when so filed in all material respects with the applicable requirements of the Exchange Act and the rules thereunder;

(v) The Underwriting Agreement has been duly authorized, executed and delivered by the Company;

(vi) The Company is not and, after giving effect to the offering and sale of the Shares and the application of the proceeds thereof as described in the Prospectus, will not be an “investment company” as defined in the Investment Company Act of 1940, as amended;

(vii) No consent, approval, authorization, filing with or order of any court or governmental agency or body is required in connection with the transactions contemplated herein, except such as have been filed or obtained under the Securities Act, filed under the Exchange Act and such as may be required under the blue sky laws of any jurisdiction in connection with the purchase and distribution of the Shares by the Underwriters in the manner contemplated in the Underwriting Agreement and in the Prospectus as to which we express no opinion;

(viii) Neither the issue and sale of the Shares nor the fulfillment of the terms of the Underwriting Agreement will (i) conflict with the Company’s Certificate of Incorporation or Bylaws, (ii) result in a breach or violation of, or imposition of any lien, charge or encumbrance upon any property or assets of the Company pursuant to the terms of any agreement or instrument to which the Company is a party or bound or to which its property is subject and which has been filed by the Company pursuant to the requirements of the Exchange Act, or (iii) violate any statute, any rule or regulation of any governmental agency or body, or to such counsel’s knowledge, any judgment, order or decree applicable to the Company of any court, regulatory body, administrative agency, governmental body, arbitrator or other authority having jurisdiction over the Company or any of its properties;

(ix) To such counsel’s knowledge, no holders of securities of the Company have rights to the registration of such securities under the Registration Statement, other than rights that have been waived in connection with the transactions contemplated by the Registration Statement;

(x) The statements in the Prospectus appearing under the sections entitled “RISK FACTORS—Risks Related to our Business—Clinical trials for our product candidates are expensive, time consuming and their outcome is

uncertain,” “—Our clinical trials may take longer to complete than we project or they may not be completed at all, “—We currently rely on third-party manufacturers and other third parties for production of our drug products and our dependence on these manufacturers may impair the development of our product candidates,” and “Our second generation ADC technology is still at an early stage of development and has not yet entered human clinical trials,” and the statements in the Annual Report on Form 10-K for the year ended December 31, 2002 in the section entitled “BUSINESS – Government Regulation” insofar as such statements purport to describe or summarize particular United States Food and Drug Administration (the “FDA”) requirements including procedures under the Federal Food, Drug and Cosmetic Act and Public Health Service Act or the FDA regulations, are accurate and complete in all material respects and fairly present the information purported to be described or summarized and insofar as such statements relate to FDA regulatory matters; and

(xi) To such counsel’s knowledge, there are no FDA enforcement actions or proceedings pending or threatened against the Company.

In addition, such counsel shall include a statement to the effect that although such counsel has not undertaken to determine independently the accuracy, completeness or fairness of any of the statements made in the Registration Statement or the Prospectus, such counsel has reviewed the Registration Statement and the Prospectus and participated in conferences with representatives of the Company, its accountants, the Underwriters and Underwriters’ counsel at which the contents of the Registration Statement and the Prospectus and related matters were discussed and reviewed. On the basis of the information which was developed in the course of the performance of the services referred to above, considered in the light of such counsel’s understanding of the applicable law, including the requirements of Form S-3, such counsel has no reason to believe that, on the date it became effective contained any untrue statement of a material fact or omitted to state any material fact required to be stated therein or necessary to make the statements therein not misleading or that the Prospectus as of its date and on the Closing Date included or includes any untrue statement of a material fact or omitted or omits to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading (in each case, other than the financial statements and other financial and statistical information contained therein, as to which we express no opinion). The limitations inherent in the independent verification of factual matters and the character of determinations involved in the registration process are such, however, that we do not assume any responsibility for the accuracy, completeness or fairness of the statements contained in the Registration Statement and the Prospectus except to the extent set forth in Paragraph (iii) above.

(g) The Representatives shall have received on each Closing Date from ▇▇▇▇▇ Day, intellectual property counsel for the Company, an opinion, addressed to the Representatives and dated such Closing Date, and stating in effect that:

(i) Such counsel represents the Company in the preparation and/or prosecution of the pending United States non-provisional patent applications

listed in Schedules A and B thereto (collectively termed the “U.S. Patent Applications”) and are generally familiar with the technology underlying the claims of such U.S. Patent Applications. Such counsel is responsible for prosecuting the PCT applications listed in Schedule C thereto and handle through appropriate foreign associates the foreign applications listed in Schedule C thereto.

(ii) Based upon such counsel’s review of the Prospectus and Registration Statement filed by the Company with the United States Securities Exchange Commission that relate to intellectual property under the captions: “RISK FACTORS—If we are unable to enforce our intellectual property rights, we may not be able to operate our business profitably. Similarly, if we fail to sustain and further build our intellectual property rights, competitors may be able to develop competing therapies,” and “We may incur substantial costs and lose important rights as a result of litigation or other proceedings relating to patent and other intellectual property rights” and “BUSINESS— Patents and Proprietary Technology” (collectively, the “IP Portions”) and review of the U.S. Patent Applications, the statements under the IP Portions, to the best of such counsel’s knowledge and solely insofar as such statements concern descriptions of legal matters related to the U.S. Patent Applications or documents related to the U.S. Patent Applications, fairly summarize in all material respects such matters or documents.

(iii) While there can be no guarantee that any particular patent application will issue as a patent, to the best of such counsel’s knowledge, each of the U.S. Patent Applications has been properly filed and is being prosecuted in the United States Patent and Trademark Office.

(iv) Except as described in the IP Portions, to the best of such counsel’s knowledge, there are no material legal or governmental proceedings, other than proceedings before the United States Patent and Trademark Office or the respective foreign patent office, pending or threatened, with respect to any of the U.S. Patent Applications or with respect to any of the foreign applications listed in Schedule C thereto.

(v) To the best of such counsel’s knowledge, the Company is the assignee of each of the U.S. patent applications listed in Schedule A thereto. Except as set forth in the IP Portions, to the best of such counsel’s knowledge, the Company has not received any notice with respect to the potential infringement of any patents of others.

(vi) Except as described in the IP Portions and without any searches or an evaluation having been conducted for the purpose of rendering this opinion, to the best of such counsel’s knowledge, the Company is not infringing any patents of others.

(vii) Such counsel handles through appropriate foreign associates the pending foreign applications listed in Schedule D thereto, and have docketed the maintenance fee and annuity deadlines for the U.S. patents, foreign patents, and foreign applications listed in Schedule D thereto.

In addition, such counsel shall state that during the course of the preparation by the Company of the IP Portions of the Registration Statement and Prospectus, such counsel has participated in various discussions with officers, directors and/or employees of the Company, Representatives and Representatives’ counsel concerning the IP Portions. The limitations inherent in the role of outside counsel are such that, except as set forth in the above opinions, such counsel cannot and have not independently verified, and are not passing upon, and do not assume responsibility for, the accuracy, completeness or fairness of the IP Portions except to the extent set forth in paragraph (ii) above. Based upon such counsel’s examination of the Registration Statement and the Prospectus with respect to the IP Portions and such counsel’s participation, inquiries and investigations set forth above, however, no facts have come to the attention of such counsel since it began representing the Company on January 1, 2004 or of the lawyers presently within ▇▇▇▇▇ Day that represented the Company while at ▇▇▇▇▇▇ & ▇▇▇▇▇▇▇ prior to January 1, 2004, that causes such counsel or such lawyers to believe that the IP Portions of the Registration Statement related to the U.S. Patent Applications, at the time such Registration Statement became effective, contained an untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading, or that the IP Portions of the Prospectus related to the U.S. Patent Applications, at the date of the Prospectus and as of the date hereof, contained an untrue statement of material fact or omitted to state a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading.

To the extent deemed advisable by such counsel, such counsel may rely as to matters of fact on certificates of responsible officers of the Company and public officials and on the opinions of other counsel satisfactory to the Representatives as to matters which are governed by laws other than the laws of the State of New York, the General Corporation Law of the State of Delaware and the Federal laws of the United States; provided that such counsel shall state that in their opinion the Underwriters and they are justified in relying on such other opinions. Copies of such certificates and other opinions shall be furnished to the Representatives and counsel for the Underwriters.

(h) The Representatives shall have received on each Closing Date from ▇▇▇▇▇▇ Godward LLP, counsel for the Representatives, an opinion, addressed to the Representatives and dated such Closing Date, and stating in effect that:

(i) The Shares have been duly authorized and, upon delivery to the Underwriters against payment therefor in accordance with the terms of the Underwriting Agreement, will be duly issued, fully paid and nonassessable.

(ii) The Underwriting Agreement has been duly authorized, executed and delivered by the Company.

(iii) The Shares conform in all material respects to the description thereof contained in the Prospectus under the caption “Description of Capital Stock.”

(iv) The Registration Statement and Prospectus comply as to form in all material respects with the requirements of the Securities Act, except that such counsel need not express an opinion with respect to the financial statements and schedules, related notes, other financial data and statistical data derived therefrom included in the Registration Statement or Prospectus.

(v) The Registration Statement is effective under the Securities Act, and to such counsel’s knowledge no stop order suspending the effectiveness of the Registration Statement has been issued and no proceedings for that purpose have been initiated or threatened by the Commission.

In addition, such counsel shall state during the course of the preparation of the Registration Statement, such counsel participated in conferences with the Representatives and with officers and other representatives of the Company, its counsel and its independent public accountants at which the contents of the Registration Statement and Prospectus were discussed; while such counsel has not independently verified and are not passing upon the accuracy, completeness or fairness of the statements made in the Registration Statement and Prospectus, except as set forth in paragraph (iii) above, on the basis of the foregoing, no facts have come to such counsel’s attention that have caused it to believe that the Registration Statement, as of the time it became effective, contained an untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary to make the statements therein not misleading, or that the Prospectus, as of its date or the date hereof, contained or contains an untrue statement of a material fact or omitted or omits to state a material fact necessary to make the statements therein, in light of the circumstances under which they were made, not misleading, except that such counsel expresses no comment with respect to the financial statements and schedules, related notes, other financial data and statistical data derived therefrom included in the Registration Statement and Prospectus.

(i) The Representatives shall have received copies of the Lock-up Agreements executed by each entity or person listed on Schedule II hereto.

(j) The Shares shall have been approved for quotation on the Nasdaq National Market.

(k) The Company shall have furnished or caused to be furnished to the Representatives such further certificates or documents as the Representatives shall have reasonably requested.

4. Covenants of the Company.

(a) The Company covenants and agrees as follows:

(i) The Company will use its best efforts to cause the Registration Statement, if not effective at the time of execution of this Agreement, and any amendments thereto, to become effective as promptly as possible. The Company shall prepare the Prospectus in a form approved by the Representatives and file such Prospectus pursuant to Rule 424(b) under the Securities Act not later than the Commission’s close of business on the second business day following the execution and delivery of this Agreement, or, if applicable, such earlier time as may be required by the Rules.

(ii) The Company shall promptly advise the Representatives in writing (A) when any post-effective amendment to the Registration Statement shall have become effective or any supplement to the Prospectus shall have been filed, (B) of any request by the Commission for any amendment of the Registration Statement or the Prospectus or for any additional information, (C) of the issuance by the Commission of any stop order suspending the effectiveness of the Registration Statement or of any order preventing or suspending the use of any preliminary prospectus or the institution or threatening of any proceeding for that purpose and (D) of the receipt by the Company of any notification with respect to the suspension of the qualification of the Shares for sale in any jurisdiction or the initiation or threatening of any proceeding for such purpose. The Company shall not file any amendment of the Registration Statement or supplement to the Prospectus or any document incorporated by reference in the Registration Statement unless the Company has furnished the Representatives a copy for its review prior to filing and shall not file any such proposed amendment or supplement to which the Representatives reasonably object. The Company shall use its best efforts to prevent the issuance of any such stop order and, if issued, to obtain as soon as possible the withdrawal thereof.

(iii) If, at any time when a prospectus relating to the Shares is required to be delivered under the Securities Act and the Rules, any event occurs as a result of which the Prospectus as then amended or supplemented would include any untrue statement of a material fact or omit to state any material fact necessary to make the statements therein in the light of the circumstances under which they were made not misleading, or if it shall be necessary to amend or supplement the Prospectus to comply with the Securities Act or the Rules, the Company promptly shall prepare and file with the Commission, subject to the

second sentence of paragraph (ii) of this Section 4(a), an amendment or supplement which shall correct such statement or omission or an amendment which shall effect such compliance.

(iv) The Company shall make generally available to its security holders and to the Representatives as soon as practicable, but not later than 45 days after the end of the 12-month period beginning at the end of the fiscal quarter of the Company during which the Effective Date occurs (or 90 days if such 12-month period coincides with the Company’s fiscal year), an earning statement (which need not be audited) of the Company, which shall satisfy the provisions of Section 11(a) of the Securities Act or Rule 158 of the Rules.

(v) The Company shall furnish to the Representatives and counsel for the Underwriters, without charge, signed copies of the Registration Statement (including all exhibits thereto and amendments thereof) and to each other Underwriter a copy of the Registration Statement (without exhibits thereto) and all amendments thereof and, so long as delivery of a prospectus by an Underwriter or dealer may be required by the Securities Act or the Rules, as many copies of any preliminary prospectus and the Prospectus and any amendments thereof and supplements thereto as the Representatives may reasonably request. If applicable, the copies of the Registration Statement and Prospectus and each amendment and supplement thereto furnished to the Underwriters will be identical to the electronically transmitted copies thereof filed with the Commission pursuant to ▇▇▇▇▇, except to the extent permitted by Regulation S-T.

(vi) The Company shall cooperate with the Representatives and their counsel in endeavoring to qualify the Shares for offer and sale in connection with the offering under the laws of such jurisdictions as the Representatives may designate and shall maintain such qualifications in effect so long as required for the distribution of the Shares; provided, however, that the Company shall not be required in connection therewith, as a condition thereof, to qualify as a foreign corporation or to execute a general consent to service of process in any jurisdiction or subject itself to taxation as doing business in any jurisdiction.

(vii) The Company, during the period when the Prospectus is required to be delivered under the Securities Act and the Rules or the Exchange Act, will file all reports and other documents required to be filed with the Commission pursuant to Section 13, 14 or 15 of the Exchange Act within the time periods required by the Exchange Act and the regulations promulgated thereunder.

(viii) Without the prior written consent of CIBC World Markets Corp. and Banc of America Securities LLC for a period of 30 days after the date of this Agreement, the Company shall not issue, sell or register with the Commission (other than on Form S-8 or on any successor form), or otherwise dispose of, directly or indirectly, any equity securities of the Company (or any securities convertible into, exercisable for or exchangeable for equity securities of

the Company), except for the issuance of the Shares pursuant to the Registration Statement and the issuance of shares pursuant to the Company’s existing stock option plans, employee stock purchase plan or bonus plan as described in the Registration Statement and the Prospectus.

(ix) On or before completion of this offering, the Company shall make all filings required under applicable securities laws and by the Nasdaq National Market (including any required registration under the Exchange Act).

(x) Prior to the Closing Date, the Company will issue no press release or other communications directly or indirectly and hold no press conference with respect to the Company, the condition, financial or otherwise, or the earnings, business affairs or business prospects of any of them, or the offering of the Shares without the prior written consent of the Representatives unless in the judgment of the Company and its counsel, and after notification to the Representatives, such press release or communication is required by law.

(xi) The Company will apply the net proceeds from the offering of the Shares in the manner set forth under “Use of Proceeds” in the Prospectus.

(b) The Company agrees to pay, or reimburse if paid by the Representatives, whether or not the transactions contemplated hereby are consummated or this Agreement is terminated, all costs and expenses incident to the public offering of the Shares and the performance of the obligations of the Company under this Agreement including those relating to: (i) the preparation, printing, filing and distribution of the Registration Statement including all exhibits thereto, each preliminary prospectus, the Prospectus, all amendments and supplements to the Registration Statement and the Prospectus and any document incorporated by reference therein, and the printing, filing and distribution of this Agreement; (ii) the preparation and delivery of certificates for the Shares to the Underwriters; (iii) the registration or qualification of the Shares for offer and sale under the securities or Blue Sky laws of the various jurisdictions referred to in Section 4(a)(vi), including the reasonable fees and disbursements of counsel for the Underwriters in connection with such registration and qualification and the preparation, printing, distribution and shipment of preliminary and supplementary Blue Sky memoranda; (iv) the furnishing (including costs of shipping and mailing) to the Representatives and to the Underwriters of copies of each preliminary prospectus, the Prospectus and all amendments or supplements to the Prospectus, and of the several documents required by this Section to be so furnished, as may be reasonably requested for use in connection with the offering and sale of the Shares by the Underwriters or by dealers to whom Shares may be sold; (v) the filing fees of the NASD in connection with its review of the terms of the public offering and reasonable fees and disbursements of counsel for the Underwriters in connection with such review; (vi) inclusion of the Shares for quotation on the Nasdaq National Market; and (vii) all transfer taxes, if any, with respect to the sale and delivery of the Shares by the Company to the Underwriters. Subject to the provisions of Section 7, the Underwriters agree to pay, whether or not the transactions contemplated hereby are consummated or this Agreement is terminated, all costs and expenses incident to the performance of the obligations of the Underwriters under this Agreement not payable by the Company pursuant to the preceding sentence, including, without limitation, the fees and disbursements of counsel for the Underwriters.

5. Indemnification.

(a) The Company agrees to indemnify and hold harmless each Underwriter and each person, if any, who controls any Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act against any and all losses, claims, damages and liabilities, joint or several (including any reasonable investigation, legal and other expenses incurred in connection with, and any amount paid in settlement of, any action, suit or proceeding or any claim asserted), to which they, or any of them, may become subject under the Securities Act, the Exchange Act or other Federal or state law or regulation, at common law or otherwise, insofar as such losses, claims, damages or liabilities arise out of or are based upon (i) any untrue statement or alleged untrue statement of a material fact contained in any preliminary prospectus, the Registration Statement or the Prospectus or any amendment thereof or supplement thereto, or in any Blue Sky application or other information or other documents executed by the Company filed in any state or other jurisdiction to qualify any or all of the Shares under the securities laws thereof (any such application, document or information being hereinafter referred to as a “Blue Sky Application”) or arise out of or are based upon 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; provided, however, that such indemnity shall not inure to the benefit of any Underwriter (or any person controlling such Underwriter) on account of any losses, claims, damages or liabilities arising from the sale of the Shares to any person by such Underwriter if such untrue statement or omission or alleged untrue statement or omission was made in such Preliminary Prospectus, the Registration Statement or the Prospectus, or such amendment or supplement thereto, or in any Blue Sky Application in reliance upon and in conformity with information furnished in writing to the Company by the Representatives on behalf of any Underwriter specifically for use therein or (ii) that with respect to the Preliminary Prospectus or Prospectus, (A) such Underwriter in fact failed to deliver to such person a copy of the Prospectus, as so amended or supplemented (excluding documents incorporated by reference therein), provided by the Company in accordance with the terms of this Agreement within the time period required by the Securities Act and (B) the losses, claims, damages or liabilities of such person arise out of, or are based upon, any untrue statement or alleged untrue statement of a material fact or omission or alleged omission and such untrue statement, alleged untrue statement, omission or alleged omission was corrected in the Prospectus, as so amended or supplemented. This indemnity agreement will be in addition to any liability which the Company may otherwise have.

(b) Each Underwriter agrees to indemnify and hold harmless the Company, and each person, if any, who controls the Company within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act, each director of the Company, and each officer of the Company who signs the Registration Statement, against any losses, claims, damages or liabilities to which such party may become subject, under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon an untrue statement or alleged

untrue statement of a material fact contained in any preliminary prospectus, the Registration Statement or the Prospectus, or any amendment or supplement thereto, or arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, in each case to the extent, but only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission was made in any preliminary prospectus, the Registration Statement or the Prospectus or any such amendment or supplement in reliance upon and in conformity with written information furnished to the Company by such Underwriter through the Representative expressly for use therein; provided, however, that the obligation of each Underwriter to indemnify the Company (including any controlling person, director or officer thereof) shall be limited to the net proceeds received by the Company from such Underwriter.

(c) Any party that proposes to assert the right to be indemnified under this Section will, promptly after receipt of notice of commencement of any action, suit or proceeding against such party in respect of which a claim is to be made against an indemnifying party or parties under this Section, notify each such indemnifying party of the commencement of such action, suit or proceeding, enclosing a copy of all papers served. No indemnification provided for in Section 5(a) or 5(b) shall be available to any party who shall fail to give notice as provided in this Section 5(c) if the party to whom notice was not given was unaware of the proceeding to which such notice would have related and was prejudiced by the failure to give such notice but the omission so to notify such indemnifying party of any such action, suit or proceeding shall not relieve it from any liability that it may have to any indemnified party for contribution or otherwise than under this Section. In case any such action, suit or proceeding shall be brought against any indemnified party and it shall notify the indemnifying party of the commencement thereof, the indemnifying party shall be entitled to participate in, and, to the extent that it shall wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with counsel reasonably satisfactory to such indemnified party, and after notice from the indemnifying party to such indemnified party of its election so to assume the defense thereof and the approval by the indemnified party of such counsel, the indemnifying party shall not be liable to such indemnified party for any legal or other expenses, except as provided below and except for the reasonable costs of investigation subsequently incurred by such indemnified party in connection with the defense thereof. The indemnified party shall have the right to employ its counsel in any such action, but the fees and expenses of such counsel shall be at the expense of such indemnified party unless (i) the employment of counsel by such indemnified party has been authorized in writing by the indemnifying parties, (ii) the indemnified party shall have been advised by counsel that there may be one or more legal defenses available to it which are different from or in addition to those available to the indemnifying party (in which case the indemnifying parties shall not have the right to direct the defense of such action on behalf of the indemnified party) or (iii) the indemnifying parties shall not have employed counsel to assume the defense of such action within a reasonable time after notice of the commencement thereof, in each of which cases the fees and expenses of counsel shall be at the expense of the indemnifying parties. Notwithstanding the foregoing, the Company shall only be obligated to pay the fees and expenses of one counsel (in addition to local counsel) to the Underwriters if the Company is obligated to retain separate counsel for

the Underwriters as an indemnified party pursuant to the preceding sentence. An indemnifying party shall not be liable for any settlement of any action, suit, and proceeding or claim effected without its written consent, which consent shall not be unreasonably withheld or delayed.

6. Contribution. In order to provide for just and equitable contribution in circumstances in which the indemnification provided for in Section 5(a) or 5(b) is due in accordance with its terms but for any reason is unavailable to or insufficient to hold harmless an indemnified party in respect to any losses, liabilities, claims, damages or expenses referred to therein, then each indemnifying party shall contribute to the aggregate losses, liabilities, claims, damages and expenses (including any investigation, legal and other expenses reasonably incurred in connection with, and any amount paid in settlement of, any action, suit or proceeding or any claims asserted, but after deducting any contribution received by any person entitled hereunder to contribution from any person who may be liable for contribution) incurred by such indemnified party, as incurred, in such proportion as is appropriate to reflect the relative benefits received by the Company on the one hand and the Underwriters on the other hand from the offering of the Shares pursuant to this Agreement or, if such allocation is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to above but also the relative fault of the Company on the one hand and the Underwriters on the other hand in connection with the statements or omissions which resulted in such losses, liabilities, claims, damages or expenses, as well as any other relevant equitable considerations. The Company, and the Underwriters agree that it would not be just and equitable if contribution pursuant to this Section 6 were determined by pro rata allocation (even if the Underwriters were treated as one entity for such purpose) or by any other method of allocation which does not take account of the equitable considerations referred to above. The aggregate amount of losses, liabilities, claims, damages and expenses incurred by an indemnified party and referred to above shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in investigating, preparing or defending against any litigation, or any investigation or proceeding by any governmental agency or body, commenced or threatened, or any claim whatsoever based upon any such untrue or alleged untrue statement or omission or alleged omission. Notwithstanding the provisions of this Section 6, (i) no Underwriter (except as may be provided in the Agreement Among Underwriters) shall be required to contribute any amount in excess of the amount by which the total price at which the shares underwritten by it and distributed to the public were offered to the public exceeds the amount of damages which such underwriter has otherwise been required to pay by reason of any such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. For purposes of this Section 6, each person, if any, who controls an Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act shall have the same rights to contribution as such Underwriter, and each director of the Company, each officer of the Company who signed the Registration Statement, and each person, if any, who controls the Company within the meaning of the Section 15 of the Securities Act or Section 20 of the Exchange Act, shall have the same rights to contribution as the Company. Any party entitled to contribution will, promptly after receipt of notice of commencement of any action, suit or proceeding against such party in respect of which a claim for contribution may be made against another party or parties under this Section 6, notify such party or parties from whom contribution may be sought, but the omission so to

notify such party or parties from whom contribution may be sought shall not relieve the party or parties from whom contribution may be sought from any other obligation it or they may have hereunder or otherwise than under this Section 6. No party shall be liable for contribution with respect to any action, suit, proceeding or claim settled without its written consent. The Underwriter’s obligations to contribute pursuant to this Section 6 are several in proportion to their respective underwriting commitments and not joint.

7. Termination.

(a) This Agreement may be terminated with respect to the Shares to be purchased on a Closing Date by the Representatives by notifying the Company at any time at or before a Closing Date in the absolute discretion of the Representatives if: (i) there has occurred any material adverse change in the securities markets or any event, act or occurrence that has materially disrupted, or in the opinion of the Representatives, will in the future materially disrupt, the securities markets or there shall be such a material adverse change in general financial, political or economic conditions or the effect of international conditions on the financial markets in the United States is such as to make it, in the judgment of the Representatives, inadvisable or impracticable to market the Shares or enforce contracts for the sale of the Shares; (ii) there has occurred any outbreak or material escalation of hostilities or other calamity or crisis the effect of which on the financial markets of the United States is such as to make it, in the judgment of the Representatives, inadvisable or impracticable to market the Shares or enforce contracts for the sale of the Shares; (iii) trading in the Shares or any securities of the Company has been suspended or materially limited by the Commission or trading generally on the New York Stock Exchange, Inc., the American Stock Exchange, Inc. or the Nasdaq National Market has been suspended or materially limited, or minimum or maximum ranges for prices for securities shall have been fixed, or maximum ranges for prices for securities have been required, by any of said exchanges or by such system or by order of the Commission, the National Association of Securities Dealers, Inc., or any other governmental or regulatory authority; or (iv) a banking moratorium has been declared by any state or Federal authority; or (v) in the judgment of the Representatives, there has been, since the time of execution of this Agreement or since the respective dates as of which information is given in the Prospectus, any material adverse change in the assets, properties, condition, financial or otherwise, or in the results of operations, business affairs or business prospects of the Company considered as a whole, whether or not arising in the ordinary course of business.

(b) If this Agreement is terminated pursuant to any of its provisions, the Company shall not be under any liability to any Underwriter, and no Underwriter shall be under any liability to the Company, except that (y) if this Agreement is terminated by the Representatives or the Underwriters because of any failure, refusal or inability on the part of the Company to comply with the terms or to fulfill any of the conditions of this Agreement, the Company will reimburse the Underwriters for all out-of-pocket expenses (including the reasonable fees and disbursements of their counsel) incurred by them in connection with the proposed purchase and sale of the Shares or in contemplation of performing their obligations hereunder and (z) no Underwriter who shall have failed or refused to purchase the Shares agreed to be purchased by it under this Agreement,

without some reason sufficient hereunder to justify cancellation or termination of its obligations under this Agreement, shall be relieved of liability to the Company or to the other Underwriters for damages occasioned by its failure or refusal.

8. Substitution of Underwriters. If any Underwriter shall default in its obligation to purchase on any Closing Date the Shares agreed to be purchased hereunder on such Closing Date, the Representatives shall have the right, within 36 hours thereafter, to make arrangements for one or more of the non-defaulting Underwriters, or any other underwriters, to purchase such Shares on the terms contained herein. If, however, the Representatives shall not have completed such arrangements within such 36-hour period, then the Company shall be entitled to a further period of thirty-six hours within which to procure another party or other parties satisfactory to the Underwriters to purchase such Shares on such terms. If, after giving effect to any arrangements for the purchase of the Shares of a defaulting Underwriter or Underwriters by the Representatives and the Company as provided above, the aggregate number of Shares which remains unpurchased on such Closing Date does not exceed one-eleventh of the aggregate number of all the Shares that all the Underwriters are obligated to purchase on such date, then the Company shall have the right to require each non-defaulting Underwriter to purchase the number of Shares which such Underwriter agreed to purchase hereunder at such date and, in addition, to require each non-defaulting Underwriter to purchase its pro rata share (based on the number of Shares which such Underwriter agreed to purchase hereunder) of the Shares of such defaulting Underwriter or Underwriters for which such arrangements have not been made; but nothing herein shall relieve a defaulting Underwriter from liability for its default. In any such case, either the Representatives or the Company shall have the right to postpone the applicable Closing Date for a period of not more than seven days in order to effect any necessary changes and arrangements (including any necessary amendments or supplements to the Registration Statement or Prospectus or any other documents), and the Company agrees to file promptly any amendments to the Registration Statement or the Prospectus which in the opinion of the Company and the Underwriters and their counsel may thereby be made necessary.

If, after giving effect to any arrangements for the purchase of the Shares of a defaulting Underwriter or Underwriters by the Representatives and the Company as provided above, the aggregate number of such Shares which remains unpurchased exceeds 10% of the aggregate number of all the Shares to be purchased at such date, then this Agreement, or, with respect to a Closing Date which occurs after the First Closing Date, the obligations of the Underwriters to purchase and of the Company, as the case may be, to sell the Option Shares to be purchased and sold on such date, shall terminate, without liability on the part of any non-defaulting Underwriter to the Company, and without liability on the part of the Company, except as provided in Sections 4(b), 5, 6 and 7. The provisions of this Section 8 shall not in any way affect the liability of any defaulting Underwriter to the Company or the nondefaulting Underwriters arising out of such default. The term “Underwriter” as used in this Agreement shall include any person substituted under this Section 8 with like effect as if such person had originally been a party to this Agreement with respect to such Shares.

9. Miscellaneous. The respective agreements, representations, warranties, indemnities and other statements of the Company and the several Underwriters, as set forth in this Agreement or made by or on behalf of them pursuant to this Agreement, shall remain in full force and effect, regardless of any investigation (or any statement as to the results thereof) made

by or on behalf of any Underwriter or the Company or any of their respective officers, directors or controlling persons referred to in Sections 5 and 6 hereof, and shall survive delivery of and payment for the Shares. In addition, the provisions of Sections 4(b), 5, 6 and 7 shall survive the termination or cancellation of this Agreement.

This Agreement has been and is made for the benefit of the Underwriters, the Company and their respective successors and assigns, and, to the extent expressed herein, for the benefit of persons controlling any of the Underwriters, or the Company, and directors and officers of the Company, and their respective successors and assigns, and no other person shall acquire or have any right under or by virtue of this Agreement. The term “successors and assigns” shall not include any purchaser of Shares from any Underwriter merely because of such purchase.

All notices and communications hereunder shall be in writing and mailed or delivered or by telephone or telegraph if subsequently confirmed in writing, (a) if to the Representatives, c/o CIBC World Markets Corp., ▇▇▇ ▇▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇▇, ▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇ Attention: Legal Department, Banc of America Securities LLC ▇ ▇▇▇▇ ▇▇^▇▇ ▇▇▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇ ▇▇▇▇ ▇▇▇▇▇ Attention: Legal Department and (b) if to the Company, (i) to its agent for service as such agent’s address appears on the cover page of the Registration Statement. with a copy to: ▇▇▇▇▇▇ ▇▇▇▇▇▇ White & ▇▇▇▇▇▇▇▇▇ LLP, ▇▇▇ ▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇▇▇ ▇▇▇▇, ▇▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇-▇▇▇▇, Attention: ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇, Fax: 206/▇▇▇-▇▇▇▇.

This Agreement shall be governed by and construed in accordance with the laws of the State of New York.

This Agreement may be signed in any number of counterparts, each of which shall be an original, with the same effect as if the signatures thereto and hereto were upon the same instrument.

Please confirm that the foregoing correctly sets forth the agreement among us.


Very truly yours,

SEATTLE GENETICS, INC.

By:		/s/ ▇▇▇▇ ▇. ▇▇▇▇▇▇▇
		▇▇▇▇ ▇. ▇▇▇▇▇▇▇, Ph.D.
Title:		President and Chief Executive Officer

Confirmed:

CIBC WORLD MARKETS CORP.

BANC OF AMERICA SECURITIES LLC

▇▇ ▇▇▇▇▇▇▇▇▇ + CO, LLC

Acting severally on behalf of itself

and as representative of the several

Underwriters named in Schedule I annexed

hereto.


By CIBC WORLD MARKETS CORP.

By:		/s/ ▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇
Name:		▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇
Title:		Managing Director, Equity Capital Markets

By BANC OF AMERICA SECURITIES LLC

By:		/s/ ▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇
Name:		▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇
Title:		Managing Director, Head of Equity Syndicate

SCHEDULE I


Name		Number of Firm Shares to Be Purchased
CIBC World Markets Corp.		2,520,000
Banc of America Securities LLC		2,362,500
▇▇ ▇▇▇▇▇▇▇▇▇ + Co, LLC		1,417,500
Delafield ▇▇▇▇▇▇▇▇▇, Inc.		140,000
Fortis Securities Inc		140,000
▇▇▇▇▇▇▇ ▇▇▇▇▇▇ ▇▇▇▇▇, Inc.		140,000
Punk, ▇▇▇▇▇▇ & Company, L.P.		140,000
▇▇▇▇▇ Fargo Securities, LLC		140,000

Total		7,000,000

Sch I - 1

SCHEDULE II

Lock-up Signatories

JPMP Capital Corp.

▇▇▇▇▇ Brothers Investments

Genentech, Inc.

Soffinova Venture Partners

▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇

▇▇▇▇▇ ▇▇▇▇▇

▇▇▇▇ ▇. ▇▇▇▇▇▇▇

▇. ▇▇▇▇▇ Fell

▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇

▇▇▇▇ ▇▇▇▇ ▇▇▇▇▇▇▇▇▇

▇▇▇ ▇. ▇▇▇▇▇▇▇

▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇

▇▇▇▇▇ ▇. ▇▇▇▇▇▇

▇▇▇▇. ▇. ▇▇▇▇▇▇▇

▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇

▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇

▇▇▇▇▇▇▇ ▇. Southern

▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇

Sch II - 1

Exhibit A

Form of

Lock-Up Agreement

January , 2004

CIBC World Markets Corp.

Banc of America Securities LLC

▇▇ ▇▇▇▇▇▇▇▇▇ + Co, LLC

As Representatives of the Several Underwriters (the “Underwriters”)

c/o CIBC World Markets Corp.

▇▇▇ ▇^▇▇ ▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇ ▇▇▇▇▇

Re: Public Offering of Common Stock of Seattle Genetics, Inc.

Ladies and Gentlemen:

The undersigned, a holder of common stock or rights to acquire Common Stock (the “Common Stock”) of Seattle Genetics, Inc. (the “Company”) wishes to facilitate the public offering of Common Stock pursuant to a Registration Statement on Form S-3, File No. 333-111269 (the “Registration Statement”) which was declared effective by the Securities and Exchange Commission (the “Commission”) on or about January 12, 2004 for the registration of shares of Common Stock with an aggregate maximum offering price of $75.0 million (the “Offering”). The undersigned further understands that CIBC World Markets Corp., Banc of America Securities LLC and ▇▇ ▇▇▇▇▇▇▇▇▇ + Co, LLC propose to enter into an Underwriting Agreement (the “Underwriting Agreement”) with the Company in connection with the Offering.

In order to induce the Company, you and the other Underwriters to enter into the Underwriting Agreement and to proceed with the Offering, the undersigned agrees, for the benefit of the Company, you and the other Underwriters, that the undersigned will not, without prior written consent of CIBC World Markets Corp. and Banc of America Securities LLC, directly or indirectly, make any offer, sale, assignment, transfer, encumbrance, contract to sell, grant of an option to purchase or other disposition of any Common Stock beneficially owned (within the meaning of Rule 13d-3 under the Securities Exchange Act of 1934, as amended) by the undersigned on the date hereof or hereafter acquired, beginning on the date hereof through the period of 90 days subsequent to the date of the Underwriting Agreement, other than Common Stock to be transferred as a gift or gifts (provided that any donee thereof agrees in writing to be bound by the terms hereof).

The undersigned confirms that he, she or it understands that the Underwriters and the Company will rely upon the representations set forth in this agreement in proceeding with the Offering. This agreement shall be binding on the undersigned and his, her or its respective successors, heirs, personal representatives and assigns. The undersigned agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent against the transfer of Common Stock or securities convertible into or exchangeable or exercisable for Common Stock held by the undersigned except in compliance with this agreement.


		Very truly yours,

Dated , 2004

		(Name of Stockholder)


		(Signature)


		(Name of Signatory if Stockholder is an entity—Please Print)


		(Title of Signatory if Stockholder is an entity—Please Print)

7,000,000 Shares Seattle Genetics, Inc. Common Stock UNDERWRITING AGREEMENT

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