<PAGE>   1
                                             * TEXT OMITTED AND FILED SEPARATELY
                                                CONFIDENTIAL TREATMENT REQUESTED
                                          UNDER 17 C.F.R. SECTIONS 200.80(b)(4),
                                                            200.83 AND 240.24b-2


                                  EXHIBIT 10.39






                                LICENSE AGREEMENT

                                     BETWEEN

                                XENOMETRIX, INC.

                                       AND

                         AURORA BIOSCIENCES CORPORATION





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                                LICENSE AGREEMENT

This Agreement is made this 17th day of April 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 Aurora Biosciences
Corporation ("ABSC"), a Delaware corporation with principal offices at 11010
Torreyana Road, San Diego, California to license certain technology.

                                    RECITALS

WHEREAS, XENO is the owner or exclusive licensee of the XENO Patents relating to
certain assays, technology and intellectual property further described herein,
and desires to license the same to ABSC; and

WHEREAS, ABSC seeks to obtain certain license rights and licensing rights under
the XENO Patents, according to the terms contained herein (the "Agreement");

Now, therefore, in consideration of the foregoing and the covenants and premises
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
          fifty percent (50%) or the maximum interest permitted by local law of
          the voting securities of the person, corporation, or other entity or a
          fifty percent (50%) or greater interest in the income of such
          corporation or other entity or the ability otherwise of the entity to
          secure that the affairs of such person, corporation or other entity
          are managed in accordance with the such entity's wishes.

     1.2. "Aurora Technology" means all Technology owned or Controlled by
          Aurora.

     1.3. "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 6.1.

     1.4. "Consideration" shall mean money, revenue, or Equity Premium.

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     1.5.  "Control" or "Controlled" means, in the context of intellectual
           property, possession by a party of the ability to grant a license or
           sublicense in accordance with the terms of this Agreement, and
           without violating the terms of any agreement by such party with any
           Third Party.

     1.6.  "Equity Premium" shall mean Consideration received by ABSC
           attributable to the sale of a security, in excess of the fair market
           value of the security, such fair market value to be measured by the
           average closing price of the security on the principal U.S. stock
           exchange upon which it trades, for the 10 trading days immediately
           prior to the sale.

     1.7.  "Field" means [ * ]

     1.8.  "Harvard License Agreement" means the license agreement between the
           President and Fellows of Harvard College and Venmark Ltd., now XENO,
           executed on January 17, 1992.

     1.9.  "Intellectual Property" means any information and data which is not
           generally known to the public, comprising: any new and useful
           process, machine, manufacture, or composition of matter, or
           improvement thereto, whether or not patentable, designs, concepts,
           algorithms, formulae, software, techniques, practices, processes,
           methods, knowledge, skill, experience, expertise and technical
           information; copyrights; trade secrets; or patent rights (including
           pending and issued any where in the world).

     1.10. "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.

     1.11. "XENO Patents" means the U.S. patents and patent applications listed
           on Exhibit A 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 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.

     1.12. "Sublicensee" means a Third Party and its Affiliates (if any) that
           have a sublicense from ABSC under the XENO Patents.


* CERTAIN CONFIDENTIAL MATERIAL CONTAINED IN THIS DOCUMENT HAS BEEN OMITTED AND
FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION PURSUANT TO RULE
24B-2 OF THE SECURITIES AND EXCHANGE COMMISSION ACT OF 1934, AS AMENDED.



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<PAGE>   4


     1.13. "Technology" means Materials, Intellectual Property or both.

     1.14. "Third Party" means any entity other than (i) ABSC and any of its
           Affiliates, and (ii) XENO and any of its Affiliates.

     1.15. "Valid Claim" means: (a) an enforceable claim under an issued patent
           within the XENO Patents, which has not (i) expired or been canceled,
           (ii) been declared invalid by an unreversed and unappealable decision
           of a court or other appropriate body of competent jurisdiction, (iii)
           been admitted to be invalid or unenforceable through reissue,
           disclaimer or otherwise, and/or (iv) been abandoned.


2.   LICENSES

     2.1. Grant of Licenses Under the XENO Patents from XENO to ABSC.

          2.1.1. Non-Exclusive License to XENO Patents. XENO hereby grants to
               ABSC and its Affiliates a non-exclusive, worldwide license in the
               Field under XENO's ownership interest in the XENO Patents to
               make, use, have made, sell, have sold, offer for sale, import,
               export or otherwise exploit any process, composition of matter or
               other invention claimed in the XENO Patents.

          2.1.2. Non-Exclusive Sublicense to XENO Patents under the Harvard
               License Agreement. XENO hereby grants to ABSC and its Affiliates
               a non-exclusive, worldwide sublicense in the Field under XENO's
               right to sublicense the XENO Patents in the Harvard License
               Agreement to make, use, have made, sell, have sold, offer for
               sale, import, export or otherwise exploit any process,
               composition of matter or other invention claimed in the XENO
               Patents. ABSC acknowledges the Harvard License Agreement and
               XENO's duties and obligations thereunder.

          2.1.3. Right to Sublicense the XENO Patents.

               2.1.3.1. XENO hereby grants ABSC the right to grant
                    non-exclusive, worldwide sublicenses in the Field to a Third
                    Party and its Affiliate(s) under XENO's ownership interest
                    in the XENO Patents to make, use, have made, sell, offer for
                    sale, import, export or otherwise exploit any process,
                    composition of matter or other invention claimed in the XENO
                    Patents.




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               2.1.3.2. XENO hereby grants ABSC the right to grant
                    non-exclusive, worldwide sublicenses in the Field to a Third
                    Party and its Affiliate(s) under XENO's right to sublicense
                    the XENO Patents in the Harvard License Agreement to make,
                    use, have made, sell, offer for sale, import, export or
                    otherwise exploit any process, composition of matter or
                    other invention claimed in the XENO Patents.

               2.1.3.3. Sublicenses under Section 2.1.3 may be granted only to
                    licensees of Aurora Technology for use in conjunction with
                    Aurora Technology. The consideration for such sublicenses is
                    set forth in Section 3. The sublicense rights in this
                    Section 2.1.3 do not include the right to sub-sublicense.

               2.1.3.4. The parties agree that ABSC hereby has the exclusive
                    right to negotiate with [ * ] for any sublicense in the
                    Field under either XENO's ownership interest in the XENO
                    Patents or XENO's right to sublicense the XENO Patents in
                    the Harvard License Agreement. If the scope of such a
                    potential license is broader than ABSC's rights of
                    sublicense herein, ABSC and XENO agree to negotiate in good
                    faith the terms of a broader sublicensing right for ABSC,
                    consistent with XENO's Third Party obligations at the time.

     2.2. Miscellaneous Licensing Provisions.

          2.2.1. Any sublicenses granted hereunder by ABSC and granted prior to
               termination, shall terminate in accordance with such sublicensing
               agreement. XENO covenants not to sue ABSC or its Affiliates or
               Sublicensees for causes of action relating to the infringement of
               XENO's intellectual property rights (including, patent,
               copyright, trademark and trade secret rights) arising out of the
               use or practice of any invention to which ABSC and its Affiliates
               and Sublicensees have a license pursuant to Article 2 for so long
               as such license is in force as effect.

3.   COMPENSATION

     3.1. Compensation for the XENO Patents License.

          3.1.1. XENO Patent Licenses and Rights. As consideration for the
               licenses and rights granted to ABSC pursuant to Sections 2.1.1
               and 2.1.2 and otherwise herein, ABSC will pay to XENO:


* CERTAIN CONFIDENTIAL MATERIAL CONTAINED IN THIS DOCUMENT HAS BEEN OMITTED AND
FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION PURSUANT TO RULE
24B-2 OF THE SECURITIES AND EXCHANGE COMMISSION ACT OF 1934, AS AMENDED.


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                           a)  [ * ] upon signing of the Agreement;

                           b)  [ * ] per calendar year license fee payable on
                               January 1, 1999 and annually thereafter and such
                               fees paid in any calendar year are creditable
                               against the annual royalty for the same calendar
                               year to be paid by ABSC under Section 3.1.1(c),
                               and

                           c)  An annual royalty calculated by multiplying a 
                               [ * ] percent [ * ] royalty rate to the
                               Consideration received by ABSC for the sale of
                               products and services that are covered by a Valid
                               Claim of the Xeno Patents within the Field on a
                               country-by-country basis; provided however, that
                               the following are not subject to such a royalty:
                               [ * ].

                           d)  No other royalties or milestones or additional
                               fees will be due pursuant to the license under
                               Sections 2.1.1 and 2.1.2. Royalty obligations of
                               Section 3.1.1 (c) will terminate on a
                               country-by-country basis.

          3.1.2. Consideration to be paid by Third Parties for XENO Patents
               sublicenses.

               3.1.2.1. For each sublicense granted by ABSC under Sections
                    2.1.3, ABSC will pay to XENO per year the greater of [ * ]
                    dollars [ * ] or [ * ] percent [ * ] of the sublicense fees
                    agreed to by ABSC and the Third Party for a given sublicense
                    per year. XENO agrees and acknowledges that ABSC may retain
                    the remainder of the sublicense fee, and ABSC shall not be
                    obligated to pay to XENO any other compensation for such
                    sublicense. Notwithstanding the foregoing, ABSC will pay to
                    XENO [ * ] per year per excluded company to which ABSC has
                    not granted a sublicense if ABSC desires to maintain the
                    exclusive rights under Section 2.1.3.4 with respect to such
                    company.

          3.1.3. Most Favored Nation for Sections 3.1.1, and 3.1.2. If prior to
               the issuance of U.S. patent application 08/374,641 XENO has or
               shall have entered into an agreement for a license of
               substantially similar scope as the license granted in Sections
               2.1.1 or 2.1.2 with a Third Party under the XENO Patents, XENO
               shall promptly notify ABSC in writing if such license is valued
               less than [ * ]. If such a license exists, ABSC shall have the
               option of substituting such terms for those set forth herein.
               Upon written notification by ABSC to XENO, ABSC will select a

* CERTAIN CONFIDENTIAL MATERIAL CONTAINED IN THIS DOCUMENT HAS BEEN OMITTED AND
FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION PURSUANT TO RULE
24B-2 OF THE SECURITIES AND EXCHANGE COMMISSION ACT OF 1934, AS AMENDED.

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consultant reasonably acceptable to XENO who will perform a confidential review
of the value of the terms of such Third Party agreement. If ABSC chooses to
substitute such terms and such substituted terms would require payments from
ABSC that have not then been made by ABSC, then ABSC shall promptly pay the same
to XENO. If ABSC chooses to substitute such terms and such substituted terms
exceed the amount owed to XENO, XENO shall credit the difference of such
overpayments to ABSC, as appropriate.

          3.1.4. Royalty Reports, and Payments. Beginning on the Effective Date,
               ABSC shall make written reports (even if there are no sales) and
               earned royalty payments to within sixty (60) days after the end
               of the each calendar quarter. This report shall state the number,
               description, and aggregate profits according to product(s) and
               service(s) during such completed calendar quarter, and resulting
               calculation pursuant to Section 3.1.1(c) of earned royalty
               payment due XENO for such completed calendar quarter. Concurrent
               with the making of each such report, ABSC shall include payment
               due XENO of royalties for the calendar quarter covered by such
               report. All such reports, payments and the like shall be kept
               confidential by XENO in accordance with provisions herein.

          3.1.5. Accounting. ABSC agrees to keep and maintain records for a
               period of three (3) years showing the manufacture, sale, use, and
               other profits according to Section 3.1.1(c). Such records will
               include general ledger records showing cash receipts and
               expenses, and records which include sufficient detail to enable
               the royalties payable hereunder by ABSC to be determined. ABSC
               further agrees to permit its relevant books and records to be
               examined by XENO confidentially pursuant to the provisions herein
               and upon reasonable written request by XENO, from time to time
               from three (3) years from the date of a transaction to the extent
               necessary to verify reports provided for in the above section
               titled royalty, reports, and payments. Such examination is to be
               made by XENO or its designee, at the expense of XENO except in
               the event that the results of the audit reveal an underreporting
               of royalties due XENO of ten percent (10%) or more in any
               calendar year, then the audit costs shall be paid by ABSC.

4.   PROTECTION AND MAINTENANCE OF PATENT RIGHTS

XENO shall use reasonable efforts to continue to prosecute the XENO Patents to
obtain the broadest claims reasonably possible and to defend and maintain the
validity and enforceability of any issued claims. XENO shall control, at its
expense, the prosecution of all XENO Patents. XENO will provide ABSC with
written updates on the status of the prosecution of the XENO Patents at least
once per year. With the consent of XENO, not to be unreasonably withheld, 

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ABSC shall have the right, but not the obligation, to bring proceedings against
the excluded companies set forth in Section 2.1.3.4 for patent infringement of
the XENO Patents or otherwise enter into a license with such excluded companies
as set forth herein. ABSC will do so at its own risk and expense. At the request
of ABSC, XENO shall give ABSC, at ABSC's expense, all reasonable assistance
required or reasonably necessary to file suit against such excluded company and
conduct any such proceeding.


5.   REPRESENTATIONS AND WARRANTIES

     5.1. Representations and Warranties of ABSC 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 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 to execute
                  and deliver this Agreement and to perform its obligations
                  hereunder.

                  Binding Agreement. This Agreement is a legal and valid
                  obligation binding upon it 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.

     5.2. Representations and Warranties of XENO.

          XENO further represents and warrants to ABSC:

                  Right to License or Sublicense. It owns or Controls under
                  valid licenses, and will use best efforts to continue to own
                  or Control under valid licenses all right, title and interest
                  in and to the XENO Patents licensed or to be licensed or
                  sublicensed hereunder, except as otherwise provided or
                  disclosed herein.

                  Patents. It has provided to ABSC a copy of each of the XENO
                  Patents issued, pending or in preparation as of the Effective
                  Date, as listed on Exhibit A and as 



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                  requested by ABSC. To the best of XENO's knowledge, there
                  are no threatened or pending actions, suits, investigations,
                  claims, or proceedings in any way relating to the XENO
                  Patents, other than prosecution proceedings not relating to
                  interference or opposition proceedings. It does not own or
                  hold license rights to any patent or patent application not
                  listed in the applicable exhibit attached hereto which, if
                  issued, would be infringed by the ABSC or its Affiliates or
                  Sublicensee's activities pursuant to the licenses granted
                  herein. To the best of XENO's knowledge, no additional
                  patent rights that claim substantially the same patentable
                  gene expression profiling subject matter as the XENO Patents
                  licensed to ABSC herein exist or would prevent ABSC from
                  practicing the patentable methods and other patentable
                  subject matter claimed in the XENO Patents as contemplated
                  by this Agreement.

     5.3  Negation of Warranties

                  Except as expressly set forth in this Agreement, XENO MAKES NO
                  REPRESENTATIONS AND EXTENDS NO WARRANTIES OF ANY KIND, EITHER
                  EXPRESS OR IMPLIED. THERE ARE NO EXPRESS OR IMPLIED WARRANTIES
                  OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, OR
                  THAT THE USE OF THE LICENSED PRODUCTS OR SERVICES WILL NOT
                  INFRINGE ANY PATENT, COPYRIGHT, TRADEMARK, OR OTHER RIGHTS OR
                  ANY OTHER EXPRESS OR IMPLED WARRANTIES.

6.   CONFIDENTIALITY

     6.1. Confidential Information. Except as expressly provided herein, the
          parties agree that, for the Term and five (5) years 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:

                  was already known to the receiving party, other than under an
                  obligation of confidentiality, at the time of disclosure;
                  was generally available to the public or otherwise part of the
                  public domain at the time of its disclosure to the receiving
                  party; 

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                  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; or

                  was lawfully disclosed to the receiving party by a person
                  other than a party hereto,

                                       or

                  was independently developed by the receiving party.

     6.2. 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
          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).

     6.3. 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 reasonably 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.

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


7.   TERMINATION

     7.1.1 This Agreement shall continue until the last expiration date of all
          patents licensed under this Agreement.




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     7.1.2 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 ninety
           (90) days prior written notice (sixty (60) days 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 a
           reasonable time.

     7.1.3 ABSC may terminate this Agreement without cause at any time by
           providing written notice to XENO of such termination and such
           termination will be effective ninety (90) days thereafter. Any
           termination pursuant to Section 7.1.3 shall not relieve ABSC of any
           obligation or liability accrued hereunder prior to such termination,
           including ABSC's obligation to pay royalties accrued or accruable.
           The licenses granted hereunder and all sublicenses granted by ABSC
           under this agreement shall terminate in the event the Agreement is
           terminated by ABSC or termination by an arbitrator for an uncured
           breach by ABSC.

     7.1.4 XENO and ABSC acknowledge that this Agreement is an "executory
           contract" as provided in Section 365(n) of Title 11, United States
           Code (the "Bankruptcy Code"). XENO acknowledges that if XENO as a
           debtor in possession or a trustee in bankruptcy in a case under the
           Bankruptcy Code rejects the Agreement, ABSC may elect to retain its
           rights under this Agreement as provided in Section 365(n) of the
           Bankruptcy Code, including a right to any embodiments of any
           technology licensed hereunder to the fullest extent permitted by law.
           XENO or such bankruptcy trustee shall not interfere with the rights
           of ABSC as provided in this Agreement, except as otherwise permitted
           by law or equity.

8.   MISCELLANEOUS

     8.1.  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 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, that ABSC and XENO may assign this Agreement as
           part of a merger or consolidation in which the surviving entity
           assumes all of ABSC's and XENO's rights and obligations hereunder or
           a sale of substantially all of the assets of such party to which this
           Agreement relates. The parties agree that in the event of the
           termination of the Harvard License Agreement, the President and
           Fellows of Harvard College shall have the option of assigning this
           Agreement to it or terminating the licenses in Sections 2.1.2 and
           2.1.3.2 together with the related obligations of ABSC under Sections
           3.1.1 and 3.1.2.



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     8.2. 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.

     8.3. Limitation of Liability. NEITHER PARTY SHALL BE LIABLE TO THE OTHER
          FOR ANY SPECIAL, CONSEQUENTIAL, INCIDENTIAL, OR INDIRECT DAMAGES
          ARISING OUT OF THIS AGREEMENT, HOWEVER CAUSED, UNDER ANY THEORY OF
          LIABILITY.

     8.4. Indemnification. ABSC 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
          attorney's fees) arising out of a suit by a Third Party from the
          performance under this Agreement by ABSC; except to the extent such
          claim is caused by the negligence or willful misconduct of XENO or a
          breach of a representation of XENO. XENO will defend, indemnify and
          hold ABSC, its officers, directors, employees, Affiliates and agents
          harmless against any and all liability, loss, damage, claim or expense
          (including attorney's fees) arising out of a suit by a Third Party
          from the performance under this Agreement by XENO; except to the
          extent such claim is caused by the negligence or willful misconduct of
          ABSC or a breach of a representation of ABSC.

     8.5. Diligence. ABSC agrees to use reasonable 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.

     8.6. 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(s), 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.

     8.7. 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 



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          ABSC. 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.

     8.8. 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).

     8.9. 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
                  Boulder, Colorado  80301-5700

                  Copies to:
                  Paul J. Koivuniemi
                  Vice President, Legal Affairs and Corporate Secretary
                  Xenometrix, Inc.
                  2425 North 55th Street
                  Boulder, Colorado  80301-5700

         For ABSC:
                  Paul A. Grayson
                  Senior Vice President, Corporate Development
                  Aurora Biosciences Corporation
                  11010 Torreyana Road
                  San Diego, CA.  92121

                  Copies to:
                  John D. Mendlein, Ph.D., J.D.
                  Vice President, Intellectual Property and Senior Legal Counsel
                  Aurora Biosciences Corporation
                  11010 Torreyana Road
                  San Diego, CA.  92121



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         Notices shall be in writing and shall be deemed delivered when
         received, if delivered by a courier, or on the second business day
         following mailing, if sent by first-class certified or registered mail,
         postage prepaid.

     8.10. 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 ABSC's president will meet
          in person or by video-conferencing in a good faith effort to resolve
          any disputes concerning this Agreement. Within thirty (30) days 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 within
          thirty (30) days 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 San Diego,
          California, if requested by XENO or in Boulder, Colorado if requested
          by ABSC. 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 


                                       14
<PAGE>   15


          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.

     8.11. Governing Law. If an arbitration is requested by XENO this Agreement
          shall be governed by and construed in accordance with the laws of the
          State of California, without regard or giving effect to its principles
          of conflict of laws. If an arbitration is requested by ABSC 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.

     8.12. 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 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, the provision of Sections 1, 2, 4, 5, 6, 7 and 8 and
          any other provision intended by its meaning to survive, will survive
          the expiration or any other termination of this Agreement.

     8.13. 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.

     8.14. 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. This Agreement will not be
          enforceable and shall have no effect if this Agreement is not executed
          by XENO on or before April 17, 1998.



                                       15
<PAGE>   16


         IN WITNESS WHEREOF, the parties have executed this Agreement.


By:    /s/ Stephen J. Sullivan                               Date:  4/17/98
       ------------------------------------                         -------
       Stephen J. Sullivan, M.B.A.
       CEO and President
       For Xenometrix, Inc.




By:    /s/  Timothy J. Rink                                  Date:  4/16/98
       ------------------------------------                         -------
       Timothy J. Rink M.D., Sc.D.
       President, CEO and Chairman
       For Aurora Biosciences Corporation


                                       16

<PAGE>   17



                                    EXHIBIT A
<TABLE>
<CAPTION>

===========================================================================================================
                            EUKARYOTIC GENE PROFILING
===========================================================================================================
       PATENT/           
   APPLICATION #         FILING DATE      COUNTRY      ISSUE DATE                  TITLE
-------------------      -----------     ---------     ----------     -------------------------------------
<S>                     <C>              <C>           <C>            <C>
      08/008,896           1/21/93          US
-------------------      -----------     ---------     ----------     -------------------------------------
      08/374,641           7/21/95          US         (Allowed).     Methods and Diagnostic Kits Utilizing
                                                                         Mammalian Stress Promoters to 
                                                                        Determine Toxicity of a Compound
-------------------      -----------     ---------     ----------     -------------------------------------
       61243/94            1/21/94       Australia
-------------------      -----------     ---------     ----------     -------------------------------------
       2154265             1/21/94        Canada
-------------------      -----------     ---------     ----------     -------------------------------------
      0 680 517            1/21/94          EPC         11/12/97
-------------------      -----------     ---------     ----------     -------------------------------------
       6-517147            1/21/94         Japan
-------------------      -----------     ---------     ----------     -------------------------------------
      9601405-5            2/13/96       Singapore
-------------------      -----------     ---------     ----------     -------------------------------------
      US94/00583           1/21/94          PCT
-------------------      -----------     ---------     ----------     -------------------------------------
   694 06 772.5-08                        Germany       11/25/97
===========================================================================================================
</TABLE>


<TABLE>
<CAPTION>

=============================================================================================================
                            BACTERIAL GENE PROFILING
=============================================================================================================
    PATENT/     
  APPLICATION #          FILING DATE      COUNTRY      ISSUE DATE                TITLE
-------------------      -----------     ---------     ----------    ----------------------------------------
<S>                     <C>             <C>          <C>            <C>   
      5,589,337            1/6/95           US          12/31/96     Methods and Diagnostic Kits for 
                                                                     Determining Toxicity Utilizing Bacterial
                                                                     Stress Promoters Fused to Report Genes
-------------------      -----------     ---------     ----------    ----------------------------------------
        651825             7/6/93           EPO          1/14/98
-------------------      -----------     ---------     ----------    ----------------------------------------
      5,585,232            4/21/94          US          12/17/96     Methods and Diagnostics Kits for 
                                                                     Determining Toxicity Utilizing E. coli 
                                                                     Stress Promoters Fused to Reporter Genes
-------------------      -----------     ---------     ----------    ----------------------------------------
      9601688-6            2/14/96       Singapore
-------------------      -----------     ---------     ----------    ----------------------------------------
      2,139,667            7/9/93         Canada
-------------------      -----------     ---------     ----------    ----------------------------------------
       6-503562            7/6/93          Japan
-------------------      -----------     ---------     ----------    ----------------------------------------
      95-700038            7/6/93          Korea
-------------------      -----------     ---------     ----------    ----------------------------------------
      07/910793            7/6/92           US
-------------------      -----------     ---------     ----------    ----------------------------------------
       45884/93            7/6/93        Australia
-------------------      -----------     ---------     ----------    ----------------------------------------
        95.004             7/6/93         Norway
=============================================================================================================
</TABLE>



                                       17