Document:

<PAGE>

                                                                    CONFIDENTIAL

                                LICENSE AGREEMENT

                                     BETWEEN

                                XENOMETRIX, INC.

                                       AND

                            ROSETTA INPHARMATICS INC.

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

<PAGE>

                                LICENSE AGREEMENT

This Agreement (this "AGREEMENT") is made this 12th day of November, 1998 (the
"EFFECTIVE Date"), by and between Xenometrix, Inc. ("XENO"), a Delaware
corporation with principal offices at 2425 North 55th Street, Boulder, CO
80301-5700 and Rosetta Inpharmatics, Inc. ("ROSETTA"), a Delaware corporation
with principal offices at 12040 115th Avenue N.E., Kirkland, WA 98034, to
license certain technology according to the terms and conditions, but subject
to the limitations, set forth in this Agreement.

                                    RECITALS

WHEREAS, XENO is the owner or exclusive licensee of the XENO Patents (as defined
below) and the Harvard Patents (as defined below) relating to certain assays,
technology and intellectual property further described herein, and desires to
non-exclusively license the same to ROSETTA; and

WHEREAS, ROSETTA seeks to obtain certain non-exclusive license rights and
sublicensing rights under the XENO Patents and the Harvard Patents, according to
the terms contained herein;

Now, therefore, in consideration of the foregoing and the covenants and promises
contained herein, the parties agree as follows:

 1.  DEFINITIONS

     1.1. "AFFILIATE" means any corporation or other business entity controlled
          by, or in common control of an entity. Control, as used in the context
          of a business entity, means the ownership directly or indirectly of
          greater than fifty percent (5 0%) of the voting securities of the
          person, corporation, or other entity.

     1.2. "CONFIDENTIAL INFORMATION" means all information, compounds, data, and
          Materials received by either party from the other party pursuant to
          this Agreement including, without limitation, technology of each
          party, subject to the exceptions set forth in Section 5.1.

     1.3.  "FIELD" means gene expression profiling and protein expression
           profiling, including but not limited to, identifying disturbances of
           cell homeostasis and related identified chemicals.

     1.4.  "HARVARD LICENSE AGREEMENT" means the license agreement between the
           President and Fellows of Harvard College ("Harvard") and Venmark
           Ltd., now XENO, executed on January 17, 1992, as amended to date,
           attached hereto as Exhibit C.

     1.5. "HARVARD PATENTS" means all patents and patent, applications listed on
          Exhibit A (Mammalian) and Exhibit B (Bacterial) hereto, including but
          not limited to any reissues, extensions, substitutions, confirmations,
          re-registrations, re-examinations, continuations, divisionals or
          continuations-in-part of the foregoing patents and patent
          applications, as well as all foreign counterparts or equivalents
          thereof.

     1.6. "MATERIALS" means any biological or chemical entity for screening or
          assays, including reagents, cells, promoters, enhancers, vectors,
          plasmids, proteins and fragments thereof, peptides, antigens,
          antibodies, antagonists, agonists, inhibitors, and chemicals.

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

<PAGE>

     1.7. "XENO PATENTS" means all the patents and patent applications listed on
          Exhibits A and B hereto, any patent applications filed prior or
          subsequent to the Effective Date that claim the benefit of an early
          filing date to any of the patent applications listed in Exhibit A and
          Exhibit B, and any reissues, extensions, substitutions, confirmations,
          re-registrations, reexaminations, continuations, divisionals or
          continuations-in-part of the foregoing patents and patent
          applications, as well as all foreign counterparts or equivalents
          thereof.

     1.8. "THIRD PARTY" means any entity other than (i) ROSETTA and any of its
          Affiliates, and (ii) XENO and any of its Affiliates.

 2.  LICENSES

     2.1. GRANT OF LICENSES UNDER THE XENO PATENTS AND THE HARVARD PATENTS FROM
XENO TO ROSETTA.

          2.1.1.  NON-EXCLUSIVE LICENSE TO XENO PATENTS. XENO hereby grants to
                  ROSETTA and its Affiliates a non-exclusive, world-wide license
                  in the Field under XENO's ownership interest in the XENO
                  Patents [***].

          2.1.2.  NON-EXCLUSIVE SUBLICENSE TO HARVARD PATENTS UNDER THE HARVARD
                  LICENSE AGREEMENT. XENO hereby grants to ROSETTA and its
                  Affiliates a non-exclusive, world-wide sublicense in the Field
                  under XENO's right to sublicense the Harvard Patents in the
                  Harvard License Agreement [***].

 3.  COMPENSATION

     3.1. COMPENSATION FOR THE XENO PATENTS LICENSE AND HARVARD PATENTS
SUBLICENSE.

          3.1.1.  LICENSES AND RIGHTS. As consideration for the licenses and
                  rights granted to ROSETTA herein, ROSETTA will pay to XENO:

                           a)       [***] upon signing of the Agreement, of
which [***]

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -3-

<PAGE>

[***]

                           b)       [***]

 4.  REPRESENTATIONS AND WARRANTIES; COVENANTS

     4.1. REPRESENTATIONS AND WARRANTIES OF ROSETTA AND XENO.

          Each party hereby represents and warrants:

                  CORPORATE POWER. Such party is duly organized and validly
                  existing and in good standing under the laws of the state
                  and/or country of its incorporation and has all requisite
                  corporate power and authority to enter into this Agreement and
                  to carry out the provisions hereof.

                  DUE AUTHORIZATION. Such party is duly authorized and has all
                  corporate power necessary to execute and deliver this
                  Agreement and to perform its obligations hereunder.

                  BINDING AGREEMENT. This Agreement is a legal and valid
                  obligation binding upon such party and enforceable in
                  accordance with its terms. The execution, delivery and
                  performance of this Agreement by such party does not conflict
                  with any agreement, instrument or understanding, oral or
                  written, to which it is a party or by which it may be bound,
                  nor violate any law or regulation of any court, governmental
                  body or administrative or other agency having jurisdiction
                  over it.

     4.2. TITLE; NO INFRINGEMENT. XENO has full title and ownership of the XENO
          Patents and XENO has all rights to the XENO Patents and the Harvard
          Patents necessary to allow it to perform its obligations as
          contemplated in thiso Agreement. The licenses and sublicenses granted
          by XENO to ROSETTA under this Agreement will in no way constitute an
          infringement or other violation of any copyright, trade secret,
          trademark, patent or other proprietary right of any third party.

     4.3. NEGATION OF WARRANTIES

                  EXCEPT AS EXPRESSLY SET FORTH IN THIS AGREEMENT, XENO MAKES NO
                  REPRESENTATIONS AND EXTENDS NO WARRANTIES OF ANY KIND, EITHER
                  EXPRESSED OR IMPLIED. EXCEPT AS EXPRESSLY SET FORTH IN THIS
                  AGREEMENT, THERE ARE NO (a) EXPRESSED OR IMPLIED WARRANTIES OF
                  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, OR TO
                  XENO'S KNOWLEDGE THAT THE USE OF THE XENO PATENTS AND HARVARD
                  PATENTS AS CONTEMPLATED IN THIS AGREEMENT WILL NOT INFRINGE
                  ANY PATENT, COPYRIGHT, TRADEMARK, OR OTHER RIGHTS OR (b) ANY
                  OTHER EXPRESSED OR IMPLIED WARRANTIES.

     4.4. HARVARD LICENSE AGREEMENT. XENO hereby represents and warrants that
          (a) [***], the Harvard License Agreement has not at the date hereof
          expired or been terminated by either XENO or Harvard and that XENO
          has not at the date hereof received nor given notice of breach or
          termination for breach of the Harvard License Agreement [***]

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -4-

<PAGE>

          neither XENO nor Harvard is in default under the Harvard
          License Agreement. XENO covenants to use best efforts to maintain the
          Harvard License Agreement from the date of this Agreement through the
          term of the Harvard License Agreement, including, but not limited to
          (c) complying with its obligations to pay the compensation due for the
          Harvard License Agreement and (d) refraining from entering into any
          modification or termination of the Harvard License Agreement that
          would in anyway affect ROSETTA's rights to the Harvard Patents under
          this Agreement. In the event that the Harvard License Agreement is
          terminated, the sublicense granted to ROSETTA by XENO pursuant to
          Section 2.1.2 with respect to [***] will survive and any further
          sublicenses granted by ROSETTA to its sublicensee with respect to
          [***] shall survive.

     4.5. INFRINGEMENT. ROSETTA hereby agrees to notify XENO immediately of any
          claim it receives for alleged patent infringement through use of XENO
          Patents Licenses and Rights.

     4.6. LICENSE AGREEMENT TO A THIRD PARTY. XENO hereby warrants that during
          the term of this Agreement XENO will not license XENO patents and/or
          sublicense Harvard License Agreement to a Third Party under financial
          and legal conditions substantially more favorable than the terms of
          the present Agreement.

5.       CONFIDENTIALITY

     5.1. CONFIDENTIAL INFORMATION. Except as expressly provided herein, the
          parties agree that, for the Term and [***] thereafter, the receiving
          party shall keep completely confidential and shall not publish or
          otherwise disclose to another party and shall not use for any purpose
          other than to perform the purposes contemplated by this Agreement any
          Confidential Information furnished to it by the disclosing party
          hereto pursuant to this Agreement, except that to the extent that it
          can be established by the receiving party by competent proof that
          such Confidential Information:

                  (a) was already known to the receiving party, other than under
                  an obligation of confidentiality, at the time of disclosure;

                  (b) was generally available to the public or otherwise part of
                  the public domain at the time of its disclosure to the
                  receiving party;

                  (c) became generally available to the public or otherwise part
                  of the public domain after its disclosure and other than
                  through any act or omission of the receiving party in breach
                  of this Agreement;

                  (d) was lawfully disclosed to the receiving party by a person
                   other than a party hereto; or

                  (e) was independently developed by the receiving party.

     5.2. PERMITTED USE AND DISCLOSURES. Each party hereto may use or disclose
          Confidential Information disclosed to it by the other party to the
          extent such use or disclosure is reasonably necessary in filing or
          prosecuting patent applications, prosecuting or defending litigation,
          complying with applicable law, governmental regulation or court order,
          submitting information to tax or other governmental authorities,
          making a permitted sublicense or otherwise exercising its rights

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -5-

<PAGE>

          hereunder, provided that if a party is required to make any such
          disclosure of another party's Confidential Information, other than
          pursuant to a confidentiality agreement, it will give reasonable
          advance notice to the latter party of such disclosure and, save to the
          extent inappropriate in the case of patent applications, will use
          reasonable efforts to secure confidential treatment of such
          information prior to its disclosure (whether through protective orders
          or otherwise).

     5.3. CONFIDENTIAL TERMS. Except as expressly provided herein, each party
          agrees not to disclose any material or financial terms of this
          Agreement to another party without the consent of the other party, not
          to be unreasonably withheld; PROVIDED, HOWEVER, each party reserves
          the right to make reasonable disclosures (including the redaction of
          material or financial terms) as required by securities or other
          applicable laws, or to actual or prospective investors or corporate
          partners (including licensees and acquirers), or to accountants,
          attorneys and other professional advisors on a need-to-know basis
          under circumstances that ensure the confidentiality thereof, or to the
          extent required by law. If such Confidential Information is to become
          public information by such disclosure the disclosing party must obtain
          the written consent of the non-disclosing party in order to obtain
          protection of the Confidential Information if necessary.

     5.4. PRESS RELEASE. Notwithstanding the foregoing, the parties shall agree
          upon a press release to announce the execution of this Agreement.
          Thereafter, XENO and ROSETTA may each disclose to Third Parties the
          information contained in such press release without the need for
          further approval by the other.

 6.  TERMINATION

     6.1.1. This Agreement shall continue until the last expiration date of all
          patents licensed under this Agreement and shall survive the
          bankruptcy, insolvency or similar event related to either party.

     6.1.2. Either party shall have the right to terminate this Agreement at any
          time for a material breach of this Agreement by the other party,
          provided that the non-breaching party shall have first given [***]
          prior written notice ([***] in the event of non-payment of any
          amounts due under this Agreement) to the breaching party describing
          such breach and stating the non-breaching party's intention to
          terminate this Agreement if such breach remains uncured, and the
          breaching party thereafter fails to cure same within [***].

     6.1.3. ROSETTA may terminate this Agreement without cause at any time by
          providing written notice to XENO of such termination and such
          termination will be effective [***] thereafter. Any termination
          pursuant to this Section 6.1.3 shall not relieve ROSETTA of any
          obligation or liability accrued hereunder prior to such termination,
          including ROSETTA's obligation to pay royalties accrued or accruable.
          The licenses granted hereunder and all sublicenses granted by
          ROSETTA under this agreement shall terminate in the event the
          Agreement is terminated by ROSETTA or termination by an arbitrator
          for an uncured breach by ROSETTA.

 7.  MISCELLANEOUS

     7.1. BINDING EFFECT; ASSIGNMENT. This Agreement shall be binding upon the
          parties' respective successors and permitted assigns. Neither party
          may assign this Agreement or any of its rights or

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -6-

<PAGE>

          obligations hereunder without the prior written consent of the other
          party (not to be unreasonably withheld), and any such attempted
          assignment shall be void; PROVIDED, HOWEVER, that ROSETTA and XENO may
          assign this Agreement as part of a merger or consolidation in which
          the surviving entity assumes all of ROSETTA's and XENO's rights and
          obligations hereunder or a sale of substantially all of the assets or
          stock of such party to which this Agreement relates. The parties
          acknowledge and agree that until the Section 8.4 Amendment is executed
          and delivered, in the event that the Harvard License Agreement is
          terminated, Harvard shall have the option of having this Agreement
          assigned to it or terminating the licenses granted herein.

     7.2. EFFECT OF WAIVER. No waiver of any default, condition, provisions or
          breach of this Agreement shall be deemed to imply or constitute a
          waiver of any other like default, condition, provision or breach of
          this Agreement.

     7.3. LIMITATION OF LIABILITY. NEITHER PARTY SHALL BE LIABLE TO THE OTHER
          FOR ANY SPECIAL, CONSEQUENTIAL, INCIDENTAL, OR INDIRECT DAMAGES
          ARISING OUT OF THIS AGREEMENT, HOWEVER CAUSED, UNDER ANY THEORY OF
          LIABILITY.

     7.4. INDEMNIFICATION. ROSETTA will defend, indemnify and hold XENO, its
          officers, directors, employees, Affiliates and agents harmless against
          any and all liability, loss, damage, claim or expense (including
          attorneys' fees) arising out of (a) a breach of any representation or
          warranty or covenant made by ROSETTA in this Agreement or (b) a suit
          by a Third Party directly relating to the negligence of ROSETTA in the
          performance under this Agreement by ROSETTA; except to the extent such
          claim is caused by the negligence or willful misconduct of XENO or a
          breach of a representation or warranty of XENO. XENO will defend,
          indemnify and hold ROSETTA, its officers, directors, employees,
          Affiliates and agents harmless against any and all liability, loss,
          damage, claim or expense (including attorneys' fees) arising out of
          (x) a breach of any representation or warranty or covenant made by
          XENQ in this Agreement or (y) a suit against ROSETTA, its officers,
          directors, employees, Affiliates or agents by a Third Party related to
          ROSETTA's performance under this Agreement. ROSETTA may, at its
          option, conduct the defense in any such suit by a Third Party and XENO
          agrees to cooperate fully with such defense.

     7.5. LIABILITY INSURANCE. ROSETTA agrees that it shall indemnify, defend,
          and hold XENO harmless from any claim, demand or action by any Third
          Party arising out of ROSETTA's gross negligence or intentional
          misconduct relating to ROSETTA's performance under this Agreement.
          ROSETTA agrees to maintain at its expense general liability coverage
          at a minimum level of [***] per occurrence, to name XENO as an
          additional insured on ROSETTA's general liability policy at all
          times during the term of this Agreement and to furnish XENO, upon
          reasonable request, certificates evidencing such coverage and
          copies of the applicable policies.

     7.6. PATENT DEFENSE COSTS. XENO will use reasonable efforts, at its
          discretion to defend XENO Patents and Harvard Patents at its own
          expense against any infringement by a Third Party, and XENO will
          notify ROSETTA promptly in writing of any such infringement by a Third
          Party known by XENO; PROVIDED, HOWEVER, that (a) ROSETTA, at its
          option, may elect to join any such prosecution of a Third Party
          infringer initiated by XENO at ROSETTA's expense and (b) XENO will
          conduct such prosecution upon the advice and consent of ROSETTA with
          respect to material decisions (including litigation strategy
          decisions) relating to such prosecution. If XENO

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -7-

<PAGE>

          does not initiate such a prosecution with respect to any individual
          instance of Third Party infringement, ROSETTA may, at its own expense,
          upon the advice and with the consent of XENO, initiate and control
          such prosecution. In the event that ROSETTA is sued by a Third Party
          for infringement of a Third Party's patent, XENO hereby agrees, if
          ROSETTA so requests, to provide ROSETTA with all reasonable advice or
          technical support that ROSETTA may reasonably request at ROSETTA's
          expense.

     7.7. DILIGENCE. ROSETTA agrees to use reasonable commercial efforts to
          fulfill the obligations of the express due diligence provision of the
          Harvard License Agreement as it applies to a sublicense under the
          Harvard License Agreement.

     7.8. FORCE MAJEURE. Neither party shall lose any rights hereunder or be
          liable to the other party for damages or losses (except for payment
          obligations) on account of failure of performance by the defaulting
          party if the failure is occasioned by war, strike, fire, act of God,
          earthquake, flood, lockout, embargo, governmental acts or orders or
          restrictions, failure of suppliers, or any other reason where failure
          to perform is beyond the reasonable control and not caused by the
          negligence or intentional conduct or misconduct of the nonperforming
          party, and such party has exerted all reasonable efforts to avoid or
          remedy such force majeure; PROVIDED HOWEVER, that in no event shall a
          party be required to settle any labor dispute or disturbance. -

     7.9. AMENDMENT. No modification, supplement to or waiver of this Agreement
          or any Addendum hereto or any of their provisions shall be binding
          upon a party hereto unless made in writing and duly signed by an
          authorized representative of both XENO and ROSETTA. In no event may
          the terms of this Agreement be changed, deleted, supplemented or
          waived by any notice, purchase order, receipt, acceptance, bill of
          lading or other similar form of document. A failure of either party to
          exercise any right or remedy hereunder, in whole or in part, or on one
          or more occasions, shall not be deemed either a waiver of such right
          or remedy to the extent not exercised, or of any other right or
          remedy, on such occasion or a waiver of any right or remedy on any
          succeeding occasion.

    7.10. ENTIRE AGREEMENT. This Agreement, and each Exhibit attached hereto,
          and each supplemental written agreement contemplated hereunder, sets
          forth the entire understanding and agreement of the parties as to the
          subject matter thereof, and there are no other understandings,
          representations or promises, written or verbal, not set forth herein
          or on which either party has relied. If any provisions of any such
          Addendum or supplemental written agreement conflict with any
          provisions set forth in this Agreement, the provisions of this
          Agreement shall take precedence, unless such Addendum or supplemental
          written agreement expressly refers to the specific provision(s) of
          this Agreement that it is intended to replace or modify (and which
          shall be limited in force and effect to such Addendum or supplemental
          written agreement only).

    7.11. NOTICES.  All Notices under this Agreement shall be given in writing
          and shall be addressed to the parties at the following addresses:

                           FOR XENO:

                                    Stephen J. Sullivan
                                    CEO, President and Director
                                    Xenometrix, Inc.
                                    2425 North 55th Street

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -8-

<PAGE>

                                    Boulder, Colorado 8030 1-5700

                            FOR ROSETTA:

                                    President
                                    Rosetta Inpharmatics
                                    12040 115th Avenue NE
                                    Kirkland, WA 98034

          Notices shall be in writing and shall be deemed delivered when
          received, if delivered by a courier, overnight mail service or the
          like, or a week following mailing, if sent by first-class certified or
          registered mail, postage prepaid.

    7.12. ARBITRATION. The parties recognize that disputes as to certain
          matters may from time to time arise during the term of this Agreement
          which relate to either party's rights and/or obligations hereunder. It
          is the objective of the parties to establish procedures to facilitate
          the resolution of disputes arising under this Agreement in an
          expedient manner by mutual cooperation and without resort to
          arbitration. The parties agree that prior to any arbitration
          concerning this Agreement, XENO's CEO and ROSETTA's CEO or COO will
          meet in person or by video-conferencing in a good faith effort to
          resolve any disputes concerning this Agreement. Within [***]
          of a formal request by either party to the other, any party may,
          by written notice to the other, have such dispute referred to their
          respective officers designated or their successors, for attempted
          resolution by good faith negotiations, such good faith negotiations to
          begin [***] after such notice is received. Except as otherwise
          provided specifically herein, any controversy or claim under
          this Agreement shall be solely settled by arbitration by one
          arbitrator pursuant to the Commercial Arbitration Rules of the
          American Arbitration Association (the "Association"); provided that
          the parties shall first use their best efforts to resolve such dispute
          by negotiation. The arbitration shall be conducted in Boulder,
          Colorado. The arbitrator shall be selected by the joint agreement of
          the parties, but if they do not so agree within twenty (20) days of
          the date of a request for arbitration, the selection shall be made
          pursuant to the rules of the Association. The decision reached by the
          arbitrator shall be conclusive and binding upon the parties hereto and
          may be filed with the clerk of any court of competent jurisdiction,
          and a judgment confirming such decision may, if desired by any party
          to the arbitration, be entered in such court. Each of the parties
          shall pay its own expenses of arbitration and the expenses of the
          arbitrator(s) shall be equally shared; PROVIDED, HOWEVER, that if in
          the opinion of the arbitrator(s) any claim hereunder or any defense or
          objection thereto was unreasonable, the arbitrator(s) may assess, as
          part of the award, all or any part of the arbitration expenses
          (including reasonable attorneys' fees) against the party raising such
          unreasonable claim, defense or objection. Nothing herein set forth
          shall prevent the parties from settling any dispute by mutual
          agreement at any time.

    7.13. GOVERNING LAW. This Agreement shall be governed by and construed in
          accordance with the laws of the State of Colorado, without regard or
          giving effect to its principles of conflict of laws.

    7.14. SEVERABILITY AND SURVIVAL. This Agreement is intended to be
          severable. If any provision(s) of this Agreement are or become
          invalid, are ruled illegal by a court of competent jurisdiction or are
          deemed unenforceable under the current applicable law from time to
          time in effect during the term hereof, it is the intention of the
          parties that the remainder of the Agreement shall not be affected
          thereby and shall continue to be construed to the maximum extent
          permitted by law at

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -9-

<PAGE>

          such time. It is further the intention of the parties that in lieu of
          each such provision which is invalid, illegal, or unenforceable, there
          shall be substituted or added as part of this .Agreement by such court
          of competent jurisdiction a provision which shall be as similar as
          possible, in economic and business objectives as intended by the
          parties to such invalid, illegal or unenforceable provision, but shall
          be valid, legal and enforceable. Unless expressly stated otherwise,
          any provision intended by its meaning to survive, will survive the
          expiration or any other termination of this Agreement.

    7.15. INDEPENDENT CONTRACTORS. The parties hereto are acting as independent
          contractors and shall not be considered partners, joint venturers or
          agents of the other. Neither shall have the right to act on behalf of,
          or to bind, the other.

    7.16. HEADINGS. Captions and paragraph headings are for convenience only
          and shall not form an interpretative part of this Agreement. Unless
          otherwise specifically provided, all references to an Article
          incorporate all Articles or subsections thereunder. This Agreement
          shall not be strictly construed against either party hereto and maybe
          executed in two or more counterparts, each of which will be deemed an
          original and the same instrument.

                            (Signature Page Follows]

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -10-

<PAGE>

                   IN WITNESS WHEREOF, the parties have executed this Agreement
as of the date first written above.

By: /s/ Stephen J. Sullivan                        Date: 11/12/98
   -------------------------------------                 ---------------------

Stephen J. Sullivan
CEO and President
For Xenometrix, Inc.

By: /s/ Stephen H. Friend, M.D., Ph.D.             Date: 11/12/98
   -------------------------------------                 ---------------------

Stephen H. Friend, M.D., Ph.D.
President, Chief Scientific Officer
for ROSETTA INPHARMATICS, Inc.

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

                                      -11-

<PAGE>

                                    EXHIBIT A

<TABLE>
<CAPTION>

         PATENT/              FILING DATE            COUNTY              ISSUE DATE                   TITLE
      APPLICATION #

    <S>                       <C>                 <C>                   <C>              <C>

                                                       [  *    *    *]

</TABLE>

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

<PAGE>

                                    EXHIBIT B

<TABLE>
<CAPTION>

         PATENT/              FILING DATE            COUNTY              ISSUE DATE                   TITLE
      APPLICATION #

      <S>                     <C>                 <C>                    <C>             <C>

                                                       [  *    *    *]

</TABLE>

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.

<PAGE>

                                    EXHIBIT C

                            HARVARD LICENSE AGREEMENT

                                      [***]

*  Material has been omitted pursuant to a request for confidential treatment,
   and such material has been filed separately with the SEC.<PAGE>

                                                                   Exhibit 10.28

                                                                       EXHIBIT B

AURORA BIOSCIENCES, INC.
390 Wakara Way, Salt Lake City, Utah 84108 o Ph: (801) 584-3431 (801) 584-3640

March 15, 1995

Jasper D. Rifle, Ph.D.
Division of Genetics
Department of Molecular and Cell Biology
Room 401, Barker Hall
University of California
Berkeley, California 94720

C. Dale Poulter, Ph.D.
Department of Chemistry
Room 2270, Eyring Building
University of Utah
Salt Lake City, Utah 84112

CONSULTING, CONFIDENTIALITY & NON-COMPETITION AGREEMENT

Dear Jasper and Dale:

This letter agreement will confirm our understanding with respect to the
consulting services you have agreed to perform for Aurora Biosciences, Inc., a
Utah corporation of which you are the scientific founding shareholders ("Aurora"
or the "Company"), as well as your obligation to maintain the confidentiality of
the Company's technology and not compete with the Company. Founders Fund, L.C.,
a Utah limited liability company that is the business founding shareholder of
the Company ("FFLC") will also agree to such confidentiality and non-competition
requirements by its execution of this letter. The parties hereto agree as
follows:

1. Consulting Services. As requested by the Company, you will perform consulting
services (the "Services") as independent contractors to the Company during your
time available to consult for commercial companies under your respective
employment arrangements with the University of California, Berkeley and the
University of Utah in the field of utilizing genetic assays to screen molecules
against intracellular disease pathways as a means of developing, and to develop,
highly selective inhibitors of enzymes regulating the prenylation of Ras protein
and biosynthesis of cholesterol for the treatment of cancer and cardiovascular
disorders (the "Field of Interest"). The exact nature and extent of your
Services will be consistent with the exclusive licensing or sponsored research
agreements to be entered into between the Company and your respective academic
institutions, as well as the needs of the Company. The compensation for your
services as scientific founders of the Company will be determined from time to
time by its Board of Directors in light of the Company's financial resources.

<PAGE>

Jasper D. Rifle, Ph.D.
C. Dale Poulter, Ph.D.
March 15,1995
Page 2

You also agree to perform Services as a member of the Company's Scientific
Advisory Board ("SAB") and advise the Company in its Field of Interest on the
same basis as other members of the Company's SAB. It is anticipated that the SAB
will meet at least twice annually for one- or two-day meetings with the
Company's scientific staff and management to discuss its research and product
development programs and long-term scientific strategy. In consideration of your
Services as a SAB member, each of you will receive the same compensation that
other members of the SAB will receive, as follows:

                  (a)      STOCK OPTIONS. Non-qualified stock options to
                           purchase 10,000 shares of the Company's common stock
                           at a price equal to the current market value ($.00l
                           per share), which options will vest in equal amounts
                           over a five-year period, as more specifically set
                           forth in the form of option certificate attached
                           hereto.

                  (b)      SAB MEETING FEE. You will receive a fee of $1,000 for
                           each day of SAB meetings you attend during the first
                           two years of your relationship with the Company and
                           $1,500 for each day of meetings during the third and
                           following years thereof.

                  (c)      RETAINER. In addition to the SAB meeting fee, you
                           will receive an annual retainer of $10,000 per year
                           upon the closing of the Company's first major
                           financing.

                  (d)      EXPENSE REIMBURSEMENT. The Company will also
                           reimburse your reasonable travel and other
                           out-of-pocket expenses incurred by you from time to
                           time at the Company's request.

Intellectual property rights that arise .from your performance of Services for
the Company under this agreement are to be transferred to the Company insofar as
such transfers are consistent with your duties to your institutional employers
and the Company's technology transfer licenses or sponsored research agreements
therewith. In this regard, you agree to disclose and assign to the Company all
of your intellectual property rights to all ideas, discoveries, inventions,
processes and improvements in the Company's Field of Interest developed by you
in the course of performing consulting Services for the Company. When requested
by the Company, you will make available to it copies of all notes, drawings,
data, and other information relating to such inventions, and will cooperate with
the Company in executing said documents (including U.S. and foreign patent
applications) concerning such rights and inventions.

2. CONFIDENTIALITY. During your performance of Services under this agreement,
you will be exposed to certain information concerning the Company's business,
products, proposed new products, designs, clinical testing programs,
manufacturing processes and techniques, customers,

<PAGE>

Jasper D. Rifle, Ph.D.
C. Dale Poulter, Ph.D.
March 15,1995
Page 3

and other information and materials that embody trade secrets or technical or
business information that is confidential and proprietary to the Company and is
not generally known to the public (collectively, "Confidential Information").
For a period of 5 years after acquiring such information, you agree not to
disclose or make use of, or allow others to use, any Confidential Information,
except to Company employees and representatives, without the Company's prior
written consent, unless such information becomes publicly available. If you are
in doubt as to whether certain information is considered confidential by the
Company, the Company upon your request will advise you as to whether such
information is confidential.

Your obligations pursuant to this section 2 shall not apply to any information
which:

                  (a)      is or hereafter becomes public knowledge by any means
                           other than your breach of the obligations set forth
                           herein;

                  (b)      the receiving party can demonstrate was in his
                           possession prior to the time of disclosure by the
                           Company;

                  (c)      the receiving party can demonstrate was received by
                           him from a third party who has the right to disclose
                           the same without any violation of any rights of or
                           obligations to the Company; or

                  (d)      the receiving party can demonstrate was independently
                           discovered or becomes public knowledge or part of the
                           public literature without benefit of the disclosure
                           of the Confidential Information by the Company.

3. PROHIBITED COMPETITION. We have discussed, and you recognize and acknowledge,
the competitive and sometimes proprietary aspects of the business of the
Company. We acknowledge your unique contributions to the Company's business and
its dependence on the research and technology which you have developed at your
respective academic institutions in the Company's Field of Interest. You
acknowledge that a business will be deemed competitive with the Company if from
time to time it performs any of the services or manufactures or sells any of the
products provided or to be offered by the Company which are based upon or
utilize your research and technology in the Company's Field of Interest or any
portion thereof (such business to be referred to as a "Competitive Business").

Accordingly, you hereby agree in consideration of the Company's agreement to (a)
engage you as a consultant to perform Services and (b) in view of the
confidential position held by you, as an officer and director of the Company and
a member of its SAB, the confidential nature and proprietary value of the
information which the Company may share with you, and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, as follows:

<PAGE>

Jasper D. Rifle, Ph.D.
C. Dale Poulter, Ph.D.
March 15,1995
Page 4

During the period you serve as an officer of the Company, a member of its Board
of Directors or its SAB, or perform consulting Services for the Company (the
"Term") and for a period of two years following the expiration or termination of
the Term (the "Restricted Term"), whether such termination is voluntary or
involuntary, you shall not, without the prior written consent of the Company:

                  (i)      For yourself or on behalf of any other person or
                           entity, directly or indirectly, either as principal,
                           agent, stockholder, employee, consultant,
                           representative or in any other capacity, own, manage,
                           operate or control, or be connected or employed by,
                           or otherwise associate in any manner with, engage in
                           or have a financial interest in any Competitive
                           Business within the United States (the "Restricted
                           Territory"); provided that nothing contained herein
                           shall preclude you from (a) employment by or other
                           affiliation with any academic institution and
                           utilizing your research and technology in the
                           Company's Field of Interest in connection therewith,
                           or (b) purchasing or owning stock in any business if
                           such stock is publicly traded and your holdings do
                           not exceed three percent (3%) of the issued and
                           outstanding capital stock of such business.

                  (ii)     Either individually or on behalf of or through any
                           third party, solicit, divert or appropriate or
                           attempt to solicit, divert or appropriate, for the
                           purpose of competing with the Company, any customers
                           or patrons of the Company, or any prospective
                           customers or patrons with respect to which the
                           Company has developed or made a sales presentation
                           (or similar offering of services), located within the
                           Restricted Territory.

                  (iii)    Either individually or on behalf of or through any
                           third party, directly or indirectly, solicit, entice
                           or persuade any employees of or consultants to the
                           Company. to leave the services of the Company for any
                           reason.

You further recognize and acknowledge that (i) the types of employment which are
prohibited by this paragraph are narrow and reasonable in relation to the skills
which represent your principal salable asset both to the Company and to your
other prospective employers, and (ii) the specific but broad geographical scope
of the provisions of this paragraph is reasonable, legitimate and fair to you in
light of the Company's need to market its services and sell its products in a
large geographic area in order to have a sufficient customer base to make the
Company's business profitable and in light of the limited restrictions on the
type of employment prohibited herein compared to the types of employment for
which you are qualified to earn your livelihood. If any part of this section 3
should be determined by a court of competent jurisdiction to be unreasonable in
duration, geographic area, or scope, then this section is intended to and shall
extend only for such period of time, in such area and with respect to such
activity as is determined to be reasonable.

<PAGE>

Jasper D. Rifle, Ph.D.
C. Dale Poulter, Ph.D.
March 15,1995
Page 5

Your obligations under this agreement shall not be affected by any termination
of your services with the Company, including termination upon the Company's
initiative, nor by any change in your position, title or function with the
Company. You hereby expressly acknowledge that any breach or threatened breach
of any of the terms and/or conditions set forth in section 3 of this agreement
will result in substantial, continuing and irreparable injury to the Company.
Therefore, you hereby agree that, in addition to any other remedy that may be
available to the Company, the Company shall be entitled to injunctive or other
equitable relief by a court of appropriate jurisdiction in the event of any
breach of threatened breach of the terms of section 3 of this agreement.

4. TERMINATION. The Company shall not terminate this agreement except for cause.
For purposes of this agreement, "cause" means a material breach of this
agreement by Jasper D. Rine, Ph.D. ("Rine") or C. Dale Poulter, Ph.D.
("Poulter"). However, the Company shall not terminate this agreement as to Rine
for a breach by Poulter nor shall it terminate this agreement as to Poulter for
a breach by Rine. Similarly, Rine shall in no way be liable or responsible for a
breach of this agreement by Poulter and Poulter shall in no way be liable or
responsible for a breach of this agreement by Rine. Rine's and Poulter's
obligations to the Company under this agreement are severable.

5. CONFLICT WITH OTHER AGREEMENTS. The Company acknowledges that Poulter and
Rine have pre-existing contractual obligations to their respective universities
regarding information pertaining to the Field of Interest and further recognizes
that state and federal law, as well as regulations and policies of Poulter's and
Rine's respective universities, may restrict their availability for providing
the Services and their ability to disclose or transfer developments relating to
the Field of Interest to the Company. All of Rine's and Poulter's obligations
under this Agreement are expressly limited by their obligations to their
respective universities and under state and federal law, whether those
obligations were pre-existing or arise hereafter. Upon request by the Company,
Poulter and Rine shall deliver their respective university's manuals, policies
or procedures relating to faculty consulting services for third parties.

6. MISCELLANEOUS. The Company hereby acknowledges that the Services are offered
by Poulter and Rine as independent contractors and not as agents of the
University of Utah or the University of California, as the case may be, and in
this regard neither the University of Utah nor

<PAGE>

Jasper D. Rifle, Ph.D.
C. Dale Poulter, Ph.D.
March 15,1995
Page 6

the University of California is responsible for any actions or omissions that
may result from the provision of Services by Poulter or Rine.

This agreement shall be governed by and construed and enforced in accordance
with the laws of the State of Utah. This agreement embodies the entire agreement
and understanding between the parties hereto and supersedes all prior oral or
written agreements and understandings relating to the subject matter hereof. No
statement, representation, warranty, covenant or agreement of any kind not set
forth in this agreement shall affect, or be used to interpret, change or
restrict, the express terms and provisions of this agreement. The Company may
assign its rights and obligations hereunder to any person or entity who succeeds
to all or substantially all of the Company's business or that aspect of the
Company's business in which you are principally involved. The rights and
obligations of Rine and Poulter under this agreement may not be assigned without
the prior written consent of the Company. This agreement shall not be modified
or amended except by ~n instrument in writing signed by or on behalf of the
parties hereto.

If the foregoing accurately sets forth your understanding of our agreement,
please so indicate by signing both copies of this letter and returning one copy
to the undersigned at the Company.

                                          Very truly yours,

                                          AURORA BIOSCIENCES, INC.

                                          By /s/
                                            -----------------------
                                             Dennis B. Farrar, President

Accept and agree to as of the date hereof:

---------------------------------------
Jasper D. Rine

---------------------------------------
C. Dale Poulter

<PAGE>

Jasper D. Rifle, Ph.D.
C. Dale Poulter, Ph.D.
March 15,1995
Page 7

Accept and agree to abide by
sections 2 and 3 of the foregoing
as to confidentiality and non-
competition as of the date hereof:

FOUNDER'S FUND, L.C.

By  /s/
  ---------------------------------

-----------------------------------
Dennis B. Farrar

   /s/
---------------------------------------
Peter D. Meldrum

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