Document:

<PAGE>

                                                                    EXHIBIT 10.2
                                                                  EXECUTION COPY

                                        OPTION AGREEMENT, dated as of May 12,
                                2003 among SEATTLE GENETICS, INC., a Delaware
                                corporation (the "Company"), and the other
                                parties hereto (each an "Optionee").

        In order to induce the Optionees to agree to purchase from the Company,
on the terms and conditions set forth in the Securities Purchase Agreement dated
as of the date hereof (the "Purchase Agreement") among the Company and the
Purchasers named therein, shares of its Series A Convertible Preferred Stock,
$.001 par value per share, and warrants (the "Warrants") to purchase shares of
the Company's common stock, $.001 par value per share (the "Common Stock"), the
Company is granting the Optionees a right and option as more fully described
herein.

        ACCORDINGLY, in consideration of the foregoing and the covenants,
agreements, representations and warranties contained in this Agreement and the
Purchase Agreement, and for other good and valuable consideration, the receipt
and sufficiency of which are hereby acknowledged by the parties, the parties
hereto hereby agree as follows:

        1.      Definitions. Capitalized terms used but not otherwise defined
herein have the meanings given to such terms in the Purchase Agreement.

        2.      Grant of Option. The Company hereby grants to the JPMP Entities
and BBI an option (exercisable in each such Optionee's sole discretion) to
purchase up to an aggregate number of shares of Series A Preferred Stock and
Warrants (the "Option Shares") that are convertible into or exercisable for, as
the case may be, the lesser of (a) 19.99% of the Common Stock or voting power of
the Company outstanding immediately prior to the closing of the transactions
contemplated by this Agreement and (b) the maximum amount of Common Stock that
the Company is permitted to sell and issue, without stockholder approval, under
Applicable Laws, including without limitation those regulations promulgated by
the National Associate of Securities Dealers, Inc. and NASDAQ (such option, the
"Option") at a purchase price set forth in Section 2.2 and Section 2.3 of the
Purchase Agreement (the "Exercise Price"). The aggregate number of Warrant
Shares issuable upon exercise of the Warrants will represent 12.5% of the Common
Stock into which the shares of Series A Preferred Stock issued hereunder are
convertible.

        3.      Option Period. The Option may be exercised in whole or in part
at any time during the period beginning on the earlier to occur of (a) the date
that is 120 days after the date of this Agreement, if the Company has not
convened the Stockholders Meeting by such date, (b) the Business Day immediately
following the date of the Stockholders Meeting, if the Company does not obtain
the Stockholder Approval thereat, or (c) the date that the Company elects to
terminate the Purchase Agreement pursuant to Section 9.1(a)(vii) of the Purchase
Agreement (such earlier date, the "Initial Exercise Date") and ending on the
date that is 10 Business Days after the Initial Exercise Date (the "Expiration
Date").

        4.      Exercise of Option. At any time after the Initial Exercise Date
and before the Expiration Date, any Optionee may send a written notice to the
Company requesting confirmation of the actual number of Option Shares. Upon
receipt of such request, the Company

<PAGE>

will send to each Optionee written notice of the number of Option Shares. Any or
all of the Optionees may exercise this Option in whole or in part by delivering
to the Company a written notice stating the number of Option Shares that such
Optionee has elected to purchase, provided that any such notice must be
countersigned in acknowledgement by all of the Optionees (whether or not
participating in such exercise).

        5.      Closing of Option. If the Option is exercised, the closing of
the issuance and sale of such shares of Series A Preferred Stock will take place
as soon as reasonably practicable (but, subject to compliance with Applicable
Laws, in no event more than 15 Business Days) after the date upon which the
Option is exercised pursuant to the terms set forth in the Purchase Agreement.

        6.      Board of Directors; Observer Rights. If the Option is exercised,
the Optionees and the Company shall modify and amend the Documents such that the
Optionees shall have the right to designate one director to the Board (the
"Optionee Director") and one representative (the "Optionee Observer") to be
present at all meetings of the Board. The Optionee Director shall be designated
by the Optionees holding a majority of the Series A Preferred Stock acquired
pursuant to this Agreement. The Optionee Observer shall be appointed by the
Optionees that are not entitled to designate the Optionee Director.

        7.      Assignment. An Optionee shall have the right to assign all or
part of its rights hereunder to any of its Affiliates.

        8.      Severability. It is the desire and intent of the parties that
the provisions of this Agreement be enforced to the fullest extent permissible
under the law and public policies applied in each jurisdiction in which
enforcement is sought. Accordingly, in the event that any provision of this
Agreement would be held in any jurisdiction to be invalid, prohibited or
unenforceable for any reason, such provision, as to such jurisdiction, shall be
ineffective, without invalidating the remaining provisions of this Agreement or
affecting the validity or enforceability of such provision in any jurisdiction.
Notwithstanding the foregoing, if such provision could be more narrowly drawn so
as not be invalid, prohibited or unenforceable in such jurisdiction, it shall,
as to such jurisdiction, be so narrowly drawn, without invalidating the
remaining provisions of this Agreement or affecting the validity or
enforceability of such provision in any other jurisdiction.

        9.      Entire Agreement. This document, together with the Securities
Purchase Agreement and any other documents referenced herein or therein,
embodies the complete agreement and understanding among the parties hereto with
respect to the subject matter hereof and supersedes and preempts any prior
understandings, agreements or representations by or among the parties, written
or oral, which may have related to the subject matter hereof in any way.

        10.     Amendments and Waivers. Any provision of this Agreement may be
amended or waived if, and only if, such amendment or waiver is in writing and
signed, in the case of an amendment, by the parties hereto and, in the case of a
waiver, by the party against whom the waiver is to be effective. No failure or
delay by either party in exercising any right, power or

                                        2

<PAGE>

privilege hereunder shall operate as a waiver thereof nor shall any single or
partial exercise thereof preclude any other or further exercise thereof or the
exercise of any other right, power or privilege. The rights and remedies herein
provided shall be cumulative and not exclusive of any rights or remedies
provided by law.

        11.     Termination. This Agreement shall terminate and be of no further
force or effect upon the earlier to occur of (i) the exercise by the Optionees
of this Option and delivery to the Optionees of the certificate evidencing the
Option Shares, (ii) the Expiration Date or (iii) the Closing Date.

        12.     Counterparts. This Agreement may be executed simultaneously in
two or more counterparts, any one of which need not contain the signatures of
more than one party, but all such counterparts taken together will constitute
one and the same agreement. It shall not be necessary in making proof of this
Agreement to produce or account for more than one such counterpart.

        13.     Remedies.

                (a)     The Optionees shall have all rights and remedies
reserved for the Optionees pursuant to this Agreement and will be entitled to
enforce such rights specifically, to recover damages by reason of any breach of
any provision of this Agreement and to exercise all other rights granted by law
or equity.

                (b)     The parties hereto agree that if any parties seek to
resolve any dispute arising under this Agreement pursuant to a legal proceeding,
the prevailing parties to such proceeding shall be entitled to receive
reasonable fees and expenses (including reasonable attorneys' fees and expenses)
incurred in connection with such proceedings.

                (c)     It is acknowledged that it will be impossible to measure
in money the damages that would be suffered if the parties fail to comply with
any of the obligations herein imposed on them and that in the event of any such
failure, an aggrieved person will be irreparably damaged and will not have an
adequate remedy at law. Any such person shall, therefore, be entitled to seek
injunctive relief, including specific performance, to enforce such obligations,
and if any action should be brought in equity to enforce any of the provisions
of this Agreement, none of the parties hereto shall raise the defense that there
is an adequate remedy at law.

        14.     Notices. The terms and provisions of Section 10.6 of the
Purchase Agreement are expressly incorporated in this Agreement .

        15.     Governing Law; Waiver of Jury Trial. All questions concerning
the construction, interpretation and validity of the Documents shall be governed
by and construed and enforced in accordance with the domestic laws of the State
of New York, without giving effect to any choice or conflict of law provision or
rule (whether in the State of New York or any other jurisdiction) that would
cause the application of the laws of any jurisdiction other than the State of
New York. In furtherance of the foregoing, the internal law of the State of New
York will control the interpretation and construction of the Documents, even if
under such jurisdiction's choice of law or conflict of law analysis, the
substantive law of some other jurisdiction would ordinarily or necessarily
apply. Notwithstanding the foregoing provisions of this Section 15, those
provisions of this Agreement that relate to the internal governance of the
Company and are required by

                                        3

<PAGE>

Delaware corporate law to be governed by such, shall be governed by and
construed and enforced in accordance with the internal laws of the State of
Delaware.

        BECAUSE DISPUTES ARISING IN CONNECTION WITH COMPLEX FINANCIAL
TRANSACTIONS ARE MOST QUICKLY AND ECONOMICALLY RESOLVED BY AN EXPERIENCED AND
EXPERT PERSON AND THE PARTIES WISH APPLICABLE LAWS TO APPLY (RATHER THAN
ARBITRATION RULES), THE PARTIES DESIRE THAT THEIR DISPUTES BE RESOLVED BY A
JUDGE APPLYING SUCH APPLICABLE LAWS. THEREFORE, TO ACHIEVE THE BEST COMBINATION
OF THE BENEFITS OF THE JUDICIAL SYSTEM AND OF ARBITRATION, THE PARTIES HERETO
WAIVE ALL RIGHT TO TRIAL BY JURY IN ANY ACTION, SUIT OR PROCEEDING BROUGHT TO
ENFORCE OR DEFEND ANY RIGHTS OR REMEDIES UNDER THIS AGREEMENT OR ANY DOCUMENTS
RELATED HERETO.

        16.     Further Assurances. Each party hereto shall do and perform or
cause to be done and performed all such further acts and things and shall
execute and deliver all such other agreements, certificates, instruments, and
documents as any other party hereto reasonably may request in order to carry out
the provisions of this Agreement and the consummation of the transactions
contemplated hereby.

        17.     Jurisdiction; Venue; Process. Any legal action or proceeding
with respect to this Agreement or the other Documents may be brought in the
courts of the State of Delaware or New York and any United States federal court
sitting in the State of Delaware or the United States of America for the
Southern District of New York and, by execution and delivery of this Agreement,
the Company hereby accepts for itself and in respect of its property, generally
and unconditionally, the jurisdiction of the aforesaid courts. The Company
hereby irrevocably waives, in connection with any such action or proceeding, any
objection, including, without limitation, any objection to the venue or based on
the grounds of forum non conveniens, which it may now or hereafter have to the
bringing of any such action or proceeding in such respective jurisdictions. The
Company hereby irrevocably consents to the service of process of any of the
aforementioned courts in any such action or proceeding by the mailing of copies
thereof by registered or certified mail, postage prepaid, to it at its address
as set forth herein. Nothing herein shall affect the right of the Optionees to
serve process in any other manner permitted by law or to commence legal
proceedings or otherwise proceed against the Company in any other jurisdiction.

        18.     Waiver. The failure of any party to enforce any of the
provisions of this Agreement will in no way be construed as a waiver of such
provisions and will not affect the right of such party thereafter to enforce
each and every provision of this Agreement in accordance with its terms.

                                    * * * * *

                                        4

<PAGE>

        IN WITNESS WHEREOF, the parties have executed this Option Agreement as
of the day and year first above written.

                                      COMPANY:

                                      SEATTLE GENETICS, INC.

                                      By:   /s/ Clay B. Siegall
                                            Name: Clay B. Siegall
                                            Title: President & CEO

                                      OPTIONEES:

                                      J.P. MORGAN PARTNERS (BHCA), L.P.

                                      By:   JPMP Master Fund Manager, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            its general partner

                                      By:   /s/ Rodney A. Ferguson
                                            Name: Rodney A. Ferguson
                                            Title: Managing Director

                                      J.P. MORGAN PARTNERS GLOBAL INVESTORS,
                                      L.P.

                                      By:   JPMP Global Investors, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            its general partner

                                      By:   /s/ Rodney A. Ferguson
                                            Name: Rodney A. Ferguson
                                            Title: Managing Director

<PAGE>

                                      J.P. MORGAN PARTNERS GLOBAL INVESTORS
                                      (CAYMAN), L.P.

                                      By:   JPMP Global Investors, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            its general partner

                                      By:   /s/ Rodney A. Ferguson
                                            Name: Rodney A. Ferguson
                                            Title: Managing Director

                                      J.P. MORGAN PARTNERS GLOBAL INVESTORS A,
                                      L.P.

                                      By:   JPMP Global Investors, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            its general partner

                                      By:   /s/ Rodney A. Ferguson
                                            Name: Rodney A. Ferguson
                                            Title: Managing Director

                                      J.P. MORGAN PARTNERS GLOBAL INVESTORS
                                      (CAYMAN) II, L.P.

                                      By:   JPMP Global Investors, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            its general partner

                                      By:   /s/ Rodney A. Ferguson
                                            Name: Rodney A. Ferguson
                                            Title: Managing Director

<PAGE>

                                      BAKER/TISCH INVESTMENTS, L.P.

                                      By:   Baker/Tisch Capital, L.P.,
                                            its general partner

                                      By:   Baker/Tisch Capital (GP), LLC,
                                            its general partner

                                      By:   /s/ Felix Baker
                                            Name: Felix Baker, Ph.D.
                                            Title: Managing Member

                                      BAKER BROS. INVESTMENTS, L.P.

                                      By:   Baker Bros. Capital, L.P.,
                                            its general partner

                                      By:   Baker Bros. Capital (GP), LLC,
                                            its general partner

                                      By: /s/ Felix Baker
                                            Name: Felix Baker, Ph.D.
                                            Title: Managing Member

                                      BAKER BROS. INVESTMENTS II, L.P.

                                      By:   Baker Bros. Capital, L.P.,
                                            its general partner

                                      By:   Baker Bros. Capital (GP), LLC,
                                            its general partner

                                      By:   /s/ Felix Baker
                                            Name: Felix Baker, Ph.D.
                                            Title: Managing Member

<PAGE>

                                      BAKER BIOTECH FUND I, L.P.

                                      By:   Baker Biotech Capital, L.P.,
                                            its general partner

                                      By:   Baker Biotech Capital (GP), LLC,
                                            its general partner

                                      By:   /s/ Felix Baker
                                            Name: Felix Baker, Ph.D.
                                            Title: Managing Member

                                      BAKER BIOTECH FUND II, L.P.

                                      By:   Baker Biotech Capital II, L.P.,
                                            its general partner

                                      By:   Baker Biotech Capital II (GP), LLC,
                                            is general partner

                                      By:   /s/ Felix Baker
                                            Name: Felix Baker, Ph.D.
                                            Title: Managing Member

                                      BAKER BIOTECH FUND II (Z), L.P.

                                      By:   Baker Biotech Capital II, L.P.,
                                            its general partner

                                      By:   Baker Biotech Capital II (GP), LLC,
                                            is general partner

                                      By:   /s/ Felix Baker
                                            Name: Felix Baker, Ph.D.
                                            Title: Managing Member<PAGE>

                                                                    EXHIBIT 10.3
                                                                  EXECUTION COPY

                                        AMENDMENT NO. 1, dated as of May 14,
                                2003 (this "Amendment No. 1"), to the Securities
                                Purchase Agreement, dated as of May 12, 2003,
                                (the "Purchase Agreement"), among SEATTLE
                                GENETICS, INC., a Delaware corporation (the
                                "Company") and the purchasers identified on
                                Schedule I to such Purchase Agreement (the
                                "Purchasers").

                                    RECITALS

                The Company and the Requisite Purchasers hereby agree to certain
amendments to the Purchase Agreement, on the terms and subject to the conditions
set forth herein.

                NOW, THEREFORE, in consideration of the mutual covenants and
agreements contained in this Amendment No. 1, the sufficiency of which is hereby
acknowledged, the parties agree as follows:

        Section 1.    Defined Terms. Capitalized terms used but not defined in
this Amendment No. 1 have the meanings ascribed to them in the Purchase
Agreement.

        Section 2.    Amendments to the Purchase Agreement.

                2.1   Section 2.1 of the Purchase Agreement is hereby amended by
deleting the number "1,600,000" appearing in said Section and inserting in lieu
thereof the number "1,640,000."

                2.2   Section 2.2 of the Purchase Agreement is hereby amended by
deleting said Section in its entirety and inserting in lieu thereof new Section
2.2:

                "Section 2.2  Authorization of Issuance of Preferred Shares and
        Warrants.

                        Subject to the Stockholder Approval, the Company has
                authorized (a) the issuance to the Purchasers at the Closing of
                an aggregate of (i) 1,640,000 shares of Series A Preferred Stock
                at a per share price of $25.00 and (ii) Warrants to purchase an
                aggregate of 2,050,000 shares of Common Stock and (b) the
                reservation of 18,450,000 Reserved Common Shares for issuance
                upon conversion of the Series A Preferred Stock and upon
                exercise of the Warrants."

                2.3   Section 2.3 of the Purchase Agreement is hereby amended by
deleting the reference to "$3,650,000" appearing in said Section and inserting
in lieu thereof the text "$3,750,000."

                2.4   Section 3.3(a) of the Purchase Agreement is hereby amended
by deleting clauses (v) and (vi) of said Section in their entirety and inserting
in lieu thereof new clauses (iv) and (v):

                "(iv) 16,400,000 shares shall be duly and validly reserved for
                issuance upon conversion of the Series A Preferred Stock, and
                (v) 2,050,000 shares shall be duly and validly reserved for
                issuance upon conversion of the Warrants."

<PAGE>

                2.5   Section 3.3(b) of the Purchase Agreement is hereby amended
by deleting the number "1,600,000" appearing in said Section and inserting in
lieu thereof the number "1,640,000."

                2.6   Schedule I to the Purchase Agreement is hereby amended by
deleting said Schedule in its entirety and inserting in lieu thereof the new
Schedule I attached hereto.

                2.7   Exhibit A to the Purchase Agreement is hereby amended by
deleting said Exhibit in its entirety and inserting in lieu thereof the new
Exhibit A, in substantially the form attached hereto.

                2.8   Exhibit C to the Purchase Agreement is hereby amended by
deleting said Exhibit in its entirety and inserting in lieu thereof the new
Exhibit C, in substantially the form attached hereto.

        Section 3.    References to the Purchase Agreement. From and after the
date hereof, all references in the Purchase Agreement and each other agreement
entered into pursuant thereto shall be deemed to be references to the Purchase
Agreement after giving effect to this Amendment No. 1.

        Section 4.    No Other Amendments. Except as expressly set forth herein,
the Purchase Agreement remains in full force and effect in accordance with its
terms and nothing contained herein shall be deemed (i) a waiver, amendment,
modification or other change of any term, condition or provision of the Purchase
Agreement or any agreement entered into pursuant to the Purchase Agreement (or a
consent to any such waiver, amendment, modification or other change), (ii) a
consent to any transaction or (iii) to prejudice any right or rights which the
Company and each of the Purchasers may have under the Purchase Agreement and/or
any agreement entered into in connection therewith.

        Section 5.    Further Assurances. The parties hereto agree to take such
further acts, to do such things, and to execute and deliver such additional
conveyances, assignments, agreements and instruments, as may be reasonably
requested in connection with the administration and enforcement of this
Amendment No. 1 and to permit the exercise thereof in compliance with any
Applicable Laws.

        Section 6.    Headings. The headings used herein are for convenience of
reference only and shall not affect the construction of, nor shall they be taken
into consideration in interpreting, this Amendment No. 1.

        Section 7.    Counterparts. This Amendment No. 1 may be executed in any
number of separate counterparts, each of which shall be an original and all of
which taken together shall constitute one and the same instrument.

        Section 8.    Applicable Law. This Amendment No. 1 shall be governed by,
and construed and interpreted in accordance with, the laws of the State of New
York.

                                    * * * * *

                                       -2-

<PAGE>

        IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 1
to be duly executed and delivered as of the day and year first above written.

                                      COMPANY:

                                      SEATTLE GENETICS, INC.

                                      By:   /s/ Clay B. Siegall
                                            Name:  Clay B. Siegall
                                            Title:  President and CEO

                                      REQUISITE PURCHASERS:

                                      J.P. MORGAN PARTNERS (BHCA), L.P.

                                      By:   JPMP Master Fund Manager, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            Its general partner

                                      By:   /s/ Rodney A. Ferguson
                                            Name:  Rodney A. Ferguson
                                            Title:  Managing Director

                                      J.P. MORGAN PARTNERS GLOBAL INVESTORS,
                                      L.P.

                                      By:   JPMP Global Investors, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            Its general partner

                                      By: /s/ Rodney A. Ferguson
                                            Name:  Rodney A. Ferguson
                                            Title: Managing Director

                                       -3-

<PAGE>

                                      J.P. MORGAN PARTNERS GLOBAL INVESTORS
                                      (CAYMAN), L.P.

                                      By:   JPMP Global Investors, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            Its general partner

                                      By: /s/ Rodney A. Ferguson
                                            Name:  Rodney A. Ferguson
                                            Title: Managing Director

                                      J.P. MORGAN PARTNERS GLOBAL INVESTORS A,
                                      L.P.

                                      By:   JPMP Global Investors, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            Its general partner

                                      By: /s/ Rodney A. Ferguson
                                            Name:  Rodney A. Ferguson
                                            Title: Managing Director

                                      J.P. MORGAN PARTNERS GLOBAL INVESTORS
                                      (CAYMAN) II, L.P.

                                      By:   JPMP Global Investors, L.P.,
                                            its general partner

                                      By:   JPMP Capital Corp.,
                                            Its general partner

                                      By: /s/ Rodney A. Ferguson
                                            Name:  Rodney A. Ferguson
                                            Title: Managing Director

                                       -4-

<PAGE>

                                      BAKER/TISCH INVESTMENTS, L.P.

                                      By:   Baker/Tisch Capital, L.P.,
                                            its general partner

                                      By:   Baker/Tisch Capital (GP), LLC,
                                            its general partner

                                      By: /s/ Felix Baker
                                            Name: Felix Baker, Ph.D.
                                            Title: Managing Member

                                      BAKER BROS. INVESTMENTS, L.P.

                                      By:   Baker Bros. Capital, L.P.,
                                            its general partner

                                      By:   Baker Bros. Capital (GP), LLC,
                                            its general partner

                                      By: /s/ Felix Baker
                                            Name: Felix Baker, Ph.D.
                                            Title: Managing Member

                                      BAKER BROS. INVESTMENTS II, L.P.

                                      By:   Baker Bros. Capital, L.P.,
                                            its general partner

                                      By:   Baker Bros. Capital (GP), LLC,
                                            its general partner

                                      By: /s/ Felix Baker
                                            Name:  Felix Baker, Ph.D.
                                            Title:  Managing Member

                                       -5-

<PAGE>

                                      BAKER BIOTECH FUND I, L.P.

                                      By:   Baker Biotech Capital, L.P.,
                                            its general partner

                                      By:   Baker Biotech Capital (GP), LLC,
                                            its general partner

                                      By: /s/ Felix Baker
                                            Name:  Felix Baker, Ph.D.
                                            Title:  Managing Member

                                      BAKER BIOTECH FUND II, L.P.

                                      By:   Baker Biotech Capital II, L.P.,
                                            its general partner

                                      By:   Baker Biotech Capital II (GP), LLC,
                                            is general partner

                                      By: /s/ Felix Baker
                                            Name:  Felix Baker, Ph.D.
                                            Title:  Managing Member

                                      BAKER BIOTECH FUND II (Z), L.P.

                                      By:   Baker Biotech Capital II, L.P.,
                                            its general partner

                                      By:   Baker Biotech Capital II (GP), LLC,
                                            is general partner

                                      By: /s/ Felix Baker
                                            Name:  Felix Baker, Ph.D.
                                            Title:  Managing Member

                                       -6-

<PAGE>

                                   SCHEDULE I

<TABLE>
<CAPTION>
                                                NUMBER OF PREFERRED     NUMBER OF          AGGREGATE
          NAME AND ADDRESS                            SHARES            WARRANTS        PRICE OF SHARES
--------------------------------------------------------------------------------------------------------
<S>                                                  <C>                 <C>           <C>
J.P. Morgan Partners (BHCA), L.P.                    512,031             640,039       $   12,800,775.00
1221 Avenue of the Americas
New York, NY  10020
Attention:  Official Notices Clerk
(fbo Srinivas Akkaraju)

with a copy to:

O'Melveny & Myers LLP
30 Rockefeller Plaza
New York, NY  10112
Telephone:  (212) 408-2400
Telecopier: (212) 408-2420
Attention:  Phillip Isom, Esq.
--------------------------------------------------------------------------------------------------------
J.P. Morgan Partners Global Investors, L.P.           81,137             101,421       $    2,028,425.00
c/o JPMP Global Investors, L.P.
c/o J.P. Morgan Partners, LLC
1221 Avenue of the Americas
New York, NY  10020
Attention:  Official Notices Clerk
(fbo Srinivas Akkaraju)

with a copy to:

O'Melveny & Myers LLP
30 Rockefeller Plaza
New York, NY  10112
Telephone:  (212) 408-2400
Telecopier: (212) 408-2420
Attention:  Phillip Isom, Esq.
--------------------------------------------------------------------------------------------------------
</TABLE>

                                       -7-

<PAGE>

<TABLE>
<CAPTION>
                                                NUMBER OF PREFERRED     NUMBER OF          AGGREGATE
          NAME AND ADDRESS                            SHARES            WARRANTS        PRICE OF SHARES
--------------------------------------------------------------------------------------------------------
<S>                                                   <C>                 <C>          <C>
J.P. Morgan Partners Global Investors
(Cayman), L.P.                                        41,182              51,478       $    1,029,550.00
c/o JPMP Global Investors, L.P.
c/o J.P. Morgan Partners, LLC
1221 Avenue of the Americas
New York, NY  10020
Attention:  Official Notices Clerk
(fbo Srinivas Akkaraju)

with a copy to:

O'Melveny & Myers LLP
30 Rockefeller Plaza
New York, NY  10112
Telephone:  (212) 408-2400
Telecopier: (212) 408-2420
Attention:  Phillip Isom, Esq.
--------------------------------------------------------------------------------------------------------
J.P. Morgan Partners Global Investors A, L.P.         11,061              13,826       $      276,525.00
c/o JPMP Global Investors, L.P.
c/o J.P. Morgan Partners, LLC
1221 Avenue of the Americas
New York, NY  10020
Attention:  Official Notices Clerk
(fbo Srinivas Akkaraju)

with a copy to:

O'Melveny & Myers LLP
30 Rockefeller Plaza
New York, NY  10112
Telephone:  (212) 408-2400
Telecopier: (212) 408-2420
Attention:  Phillip Isom, Esq.
--------------------------------------------------------------------------------------------------------
</TABLE>

                                       -8-

<PAGE>

<TABLE>
<CAPTION>
                                                NUMBER OF PREFERRED     NUMBER OF          AGGREGATE
          NAME AND ADDRESS                            SHARES            WARRANTS        PRICE OF SHARES
--------------------------------------------------------------------------------------------------------
<S>                                                   <C>                 <C>          <C>
J.P. Morgan Partners Global Investors
(Cayman) II, L.P.                                      4,589               5,736       $      114,725.00
c/o JPMP Global Investors, L.P.
c/o J.P. Morgan Partners, LLC
1221 Avenue of the Americas
New York, NY  10020
Attention:  Official Notices Clerk
(fbo Srinivas Akkaraju)

with a copy to:

O'Melveny & Myers LLP
30 Rockefeller Plaza
New York, NY  10112
Telephone:  (212) 408-2400
Telecopier: (212) 408-2420
Attention:  Phillip Isom, Esq.
--------------------------------------------------------------------------------------------------------
Baker/Tisch Investments, L.P.                         39,650              49,563       $         991,250
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Felix Baker

with a copy to:

Baker Brothers Investments
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Leo Kirby
--------------------------------------------------------------------------------------------------------
Baker Bros. Investments, L.P.                         26,780              33,475       $         669,500
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Felix Baker

with a copy to:

Baker Brothers Investments
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Leo Kirby
--------------------------------------------------------------------------------------------------------
</TABLE>

                                       -9-

<PAGE>

<TABLE>
<CAPTION>
                                                NUMBER OF PREFERRED     NUMBER OF          AGGREGATE
          NAME AND ADDRESS                            SHARES            WARRANTS        PRICE OF SHARES
--------------------------------------------------------------------------------------------------------
<S>                                                   <C>                 <C>          <C>
Baker Bros. Investments II, L.P.                      27,625              34,531       $         690,625
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Felix Baker

with a copy to:

Baker Brothers Investments
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Leo Kirby
--------------------------------------------------------------------------------------------------------
Baker Biotech Fund I, L.P.                           271,830             339,788       $       6,795,750
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Felix Baker

with a copy to:

Baker Brothers Investments
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Leo Kirby
--------------------------------------------------------------------------------------------------------
Baker Biotech Fund II, L.P.                          249,730             312,162       $       6,243,250
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Felix Baker

with a copy to:

Baker Brothers Investments
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Leo Kirby
--------------------------------------------------------------------------------------------------------
</TABLE>

                                      -10-

<PAGE>

<TABLE>
<CAPTION>
                                                NUMBER OF PREFERRED     NUMBER OF          AGGREGATE
          NAME AND ADDRESS                            SHARES            WARRANTS        PRICE OF SHARES
--------------------------------------------------------------------------------------------------------
<S>                                                  <C>                 <C>           <C>
Baker Biotech Fund II (Z), L.P.                       34,385              42,981       $         859,625
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Felix Baker

with a copy to:

Baker Brothers Investments
667 Madison Avenue, 17th Floor
New York, New York 10021
Facsimile:  (212) 521-2245
Attention:  Leo Kirby
--------------------------------------------------------------------------------------------------------
BAVP, L.P.                                           100,000             125,000       $       2,500,000
c/o BA Venture Partners
950 Tower Lane
Suite 700
Foster City, CA  94404
Attention:  Louis C. Bock
--------------------------------------------------------------------------------------------------------
Delphi Ventures VI, L.P./1/                          200,000             250,000       $       5,000,000
c/o Delphi Ventures
3000 Sand Hill Rd.
Bldg. 1, Ste. 135
Menlo Park, CA 94025
(650) 854-9650
(650) 854-2961 fax
Attention: Deepa Pakianathan
--------------------------------------------------------------------------------------------------------
Delphi BioInvestments VI, L.P.
c/o Delphi Ventures
3000 Sand Hill Rd.
Bldg. 1, Ste. 135
Menlo Park, CA 94025
(650) 854-9650
(650) 854-2961 fax
Attention: Deepa Pakianathan
--------------------------------------------------------------------------------------------------------
</TABLE>

----------
/1/ Prior to Closing, a portion of the shares of Preferred Stock and Warrants
being purchased by Delphi Ventures VI, L.P. will be allocated to Delphi
BioInvestments VI, L.P.

                                      -11-

<PAGE>

<TABLE>
<CAPTION>
                                                NUMBER OF PREFERRED     NUMBER OF          AGGREGATE
          NAME AND ADDRESS                            SHARES            WARRANTS        PRICE OF SHARES
--------------------------------------------------------------------------------------------------------
<S>                                                <C>                 <C>             <C>
T. Rowe Price Health Sciences Fund, Inc.              40,000              50,000       $       1,000,000
c/o T. Rowe Price Associates, Inc.
100 E. Pratt Street
Baltimore, MD 21202
Facsimile:  410-539-8471
Attention: Bonnie Maher

with a copy to:

Darrell N. Braman
Associate Legal Counsel
100 E. Pratt Street
Baltimore, MD 21202
Facsimile:  410-539-8471
Facsimile:  410-345-6575
--------------------------------------------------------------------------------------------------------
Total                                              1,640,000           2,050,000       $      41,000,000
--------------------------------------------------------------------------------------------------------
</TABLE>

                                      -12-

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