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                                                                   EXHIBIT 99.9













                  RESEARCH COLLABORATION AND LICENSE AGREEMENT

                                 BY AND BETWEEN

                        TEXAS BIOTECHNOLOGY CORPORATION

                                      AND

                              SCHERING CORPORATION

                                     DATED

                                 JUNE 30, 2000


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                               TABLE OF CONTENTS


                                                                         PAGE

I.       DEFINITIONS

         1.1      Additional Development Candidate.........................2
         1.2      Affiliate................................................2
         1.3      [*]......................................................2
         1.4      [*]......................................................2
         1.5      [*]......................................................2
         1.6      [*]......................................................2
         1.7      Calendar Quarter.........................................3
         1.8      Calendar Year............................................3
         1.9      Combination Product......................................3
         1.10     Development Candidate....................................3
         1.11     Field....................................................3
         1.12     First Commercial Sale....................................3
         1.13     FTE......................................................3
         1.14     Good Laboratory Practices................................3
         1.15     HRD......................................................4
         1.16     Improvement..............................................4
         1.17     IND......................................................4
         1.18     International Agreement..................................4
         1.19     Joint Invention..........................................4
         1.20     Licensed Compounds.......................................4
         1.21     Licensed Product(s) .....................................4
         1.22     Material(s) .............................................4
         1.23     NDA......................................................5
         1.24     Net Sales................................................5
         1.25     [*]......................................................6
         1.26     Proprietary Information..................................6
         1.27     Regulatory Approval......................................6
         1.28     Research Committee.......................................6
         1.29     Research Inventions......................................6
         1.30     Research Plan............................................6
         1.31     Research Program.........................................6
         1.32     Research Term............................................6
         1.33     Schering Know-How........................................7
         1.34     TBC Invention............................................7
         1.35     Territory................................................7
         1.36     Valid Claim..............................................7
         1.37     VLA-4....................................................7
         1.38     VLA-4 Compound...........................................7

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         1.39     VLA-4 Know-How............................................7
         1.40     VLA-4 Patent Rights.......................................8

II.      RESEARCH PROGRAM

         2.1      General...................................................8
         2.2      Performance of Research Program...........................8
         2.3      Research Committee........................................9
         2.4      Know-How Disclosures......................................11
         2.5      Records and Reports.......................................11
         2.6      Research Inventions.......................................12
         2.7      License of Research Inventions............................12
         2.8      Research Term.............................................12
         2.9      Termination of Research Program...........................13

III.     LICENSE

         3.1      License Grant.............................................13
         3.2      Right to Sublicense.......................................14
         3.3      License to TBC............................................14
         3.4      Restriction on Disposition of Licensed Compound...........14
         3.5      Option to [*].............................................14

IV.      DEVELOPMENT AND COMMERCIALIZATION

         4.1      Schering's Development Obligations........................15
         4.2      [*].......................................................16
         4.3      Discontinuance of Development.............................16
         4.4      [*].......................................................17
         4.5      Provision of Information..................................17
         4.6      [*].......................................................17
         4.7      [*].......................................................18
 .
V.       PAYMENTS; ROYALTIES AND REPORTS

         5.1      Additional Payment Obligations............................18
         5.2      Research Program Funding..................................18
         5.3      Consideration for License.................................19
         5.4      Milestone Payments........................................19
         5.5      [*].......................................................19
         5.6      Royalties.................................................20

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[*] Designates portions of this document that have been omitted pursuant to a
    request for confidential treatment filed with the Commission.


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         5.7      Reports; Payment Exchange Rate and Currency Conversation..21
         5.8      Maintenance of Records; Audits............................22
         5.9      Income Tax Withholding....................................23
         5.10     Direct Affiliate Licenses.................................24
         5.11     Animal Health Indications.................................24

VI .     PATENTS

         6.1      Filing, Prosecution and Maintenance of Patents............24
         6.2      [*].......................................................25
         6.3      Enforcement...............................................26
         6.4      Infringement and Third Party Licenses.....................27
         6.5      Third Party Infringement Suit.............................28
         6.6      Abandonment...............................................28
         6.7      Patent Term Restoration...................................28
         6.8      Notices Regarding Patents.................................28

VII.     CONFIDENTIALITY AND PUBLICATION

         7.1      Confidentiality...........................................29
         7.2      Return of Confidential Information........................30
         7.3      No Publicity..............................................30
         7.4      Publication...............................................31

VIII.    REPRESENTATIONS AND WARRANTIES

         8.1      Representations and Warranties of Each Party..............31
         8.2      TBC's Representations.....................................32
         8.3      Schering's Representations................................33
         8.4      No Inconsistent Agreements................................34
         8.5      Representations by Legal Counsel..........................34

IX .     INDEMNIFICATION AND LIMITATION ON LIABILITY

         9.1      Indemnification by Schering...............................34
         9.2      Indemnification by TBC....................................35
         9.3      Conditions to Indemnification.............................35
         9.4      Settlements...............................................35
         9.5      Limitation of Liability...................................36
         9.6      Insurance.................................................36

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[*] Designates portions of this document that have been omitted pursuant to a
    request for confidential treatment filed with the Commission.


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X.       TERM AND TERMINATION

         10.1     Term and Expiration.......................................36
         10.2     Termination by Schering...................................36
         10.3     Termination...............................................37
         10.4     Effect of Termination.....................................38
         10.5     Effect of New Developments................................39

XI.      MISCELLANEOUS

         11.1     Assignment/Change of Control..............................39
         11.2     Governing Law.............................................42
         11.3     Waiver....................................................42
         11.4     Independent Relationship..................................42
         1.5      Export Control............................................42
         11.6     Entire Agreement; Amendment...............................42
         11.7     Notices...................................................43
         11.8     Provisions for Insolvency.................................44
         11.9     Force Majeure.............................................45
         11.10    Severability..............................................46
         11.11    Counterparts..............................................46
         11.12    Captions..................................................46
         11.13    Recording.................................................46
         11.14    Further Actions...........................................46


SCHEDULES

1.10     Development Criteria
1.24     Schedule of Fully Allocated Manufacturing Costs
1.30     Research Plan
1.40     VLA-4 Patent Rights
5.7      Policy of Bookkeeping Exchange Rates
11.2     [*]

[*] designates portions of this document that have been omitted pursuant to a
request for confidential treatment filed with the Commission.


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                  RESEARCH COLLABORATION AND LICENSE AGREEMENT

         THIS RESEARCH COLLABORATION AND LICENSE AGREEMENT (the "Agreement") is
made effective as of June 30, 2000 (the "Effective Date"), by and between TEXAS
BIOTECHNOLOGY CORPORATION., a corporation organized and existing under the laws
of Delaware and having its principal place of business at 7000 Fannin, Houston,
TX 77030 (hereinafter referred to as "TBC") and SCHERING CORPORATION, a New
Jersey corporation having its principal place of business at 2000 Galloping
Hill Road, Kenilworth, NJ 07033, U.S.A. (hereinafter referred to as
"Schering"). TBC and Schering are sometimes referred to herein individually as
a party and collectively as the parties. References to "Schering" and "TBC"
shall include their respective Affiliates (as hereinafter defined).

         WHEREAS TBC has developed certain VLA-4 Know-How and Materials
relating to VLA-4 Compounds (each as hereinafter defined); and

         WHEREAS TBC desires to initiate a program to optimize and commercially
develop such VLA-4 Compounds; and

         WHEREAS Schering desires to enter into a research program to identify,
optimize and commercially develop VLA-4 Compounds; and

         WHEREAS Schering and TBC desire to enter into a research collaboration
to discover and develop Licensed Product(s) (as hereinafter defined) upon the
terms and conditions set forth herein; and

         WHEREAS Schering desires to obtain, and TBC is willing to grant to
Schering, a license under the VLA-4 Patent Rights and to use the VLA-4
Know-How, upon the terms and conditions set forth herein; and

         WHEREAS TBC and Schering-Plough Ltd., an Affiliate of Schering
(hereinafter referred to as "SP Ltd.") have entered into a contemporaneous
Research Collaboration and License Agreement relating to the countries and
territories outside the United States (the "International Agreement").

         NOW, THEREFORE, in consideration of the foregoing premises and the
mutual covenants herein contained, Schering and TBC hereby agree as follows:

ARTICLE I - DEFINITIONS

         As used in this Agreement, the following capitalized terms, whether
used in the singular or plural, shall have the respective meanings set forth
below:

     1.1 "Additional Development Candidate" shall have the meaning set forth in
Section 2.9

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     1.2 "Affiliate" shall mean any individual or entity directly or indirectly
controlling, controlled by or under common control with, a party to this
Agreement. For purposes of this Agreement, the direct or indirect ownership of
fifty percent (50%) or more of the outstanding voting securities of an entity,
or the right to receive fifty percent (50%) or more of the profits or earnings
of an entity shall be deemed to constitute control. Such other relationship as
in fact results in actual control over the management, business and affairs of
an entity shall also be deemed to constitute control.

     1.3 [*]

     1.4 [*]

     1.5 [*]

     1.6 [*]

     1.7 "Calendar Quarter" shall mean the respective periods of three (3)
consecutive calendar months ending on March 31, June 30, September 30 and
December 31, for so long as this Agreement is in effect.

     1.8 "Calendar Year" shall mean each successive period of twelve (12)
months commencing on January 1 and ending on December 31, for so long as this
Agreement is in effect.

     1.9 "Combination Product" shall mean a Licensed Product which comprises
two (2) or more active ingredients at least one (1) of which is a Licensed
Compound covered by a Valid Claim.

     1.10 "Development Candidate" shall mean any VLA-4 Compound which meets the
criteria for development set forth in Schedule 1.10. [*].

     1.11 "Field" shall mean the use of VLA-4 Compounds to treat or prevent any
disease, disorder or condition in humans or animals.

     1.12 "First Commercial Sale" shall mean, with respect to any Licensed
Product, the first sale for end use of such Licensed Product in a country in
the Territory after receipt of the requisite Regulatory Approval.

     1.13 "FTE" shall mean an effort substantially equivalent to one (1)
full-time research personnel dedicated for a period of one year, based, in
general, on an eight-hour workday and a 48-week working year.

     1.14 "Good Laboratory Practices" shall mean the standards and practices
recommended by the International Conference on Harmonisation (as varied from
time to time) regulating the non-human testing of pharmaceutical products.

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


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     1.15 "HRD" shall mean a health registration dossier or its equivalent
covering a Licensed Product filed in any country in the Territory and which is
analogous to an NDA and including, where applicable, applications for pricing,
pricing reimbursement approval, labeling and Regulatory Approval.

     1.16 "Improvement" shall mean any enhancement in the manufacture,
formulation, ingredients, preparation, presentation, means of delivery, dosage,
or packaging of, or any new therapeutic indications for, Licensed Product.

     1.17 "IND" shall mean an investigational new drug application or its
equivalent filed with the United States Food and Drug Administration for
beginning clinical trials in humans, or any comparable application filed with
the regulatory authorities of a country other than the United States prior to
beginning clinical trials in humans in that country, with respect to Licensed
Product(s).

     1.18 "International Agreement" shall have the meaning set forth in the
sixth recital hereof.

     1.19 "Joint Invention" shall have the meaning set forth in Section
2.6.1.19

     1.20 "Licensed Compound(s)" shall mean any VLA-4 Compound [*].

     1.21 "Licensed Product(s)" shall mean any form or dosage of pharmaceutical
compositions or preparations, including, without limitation, Combination
Products, in final form for sale by prescription, over-the-counter or any other
method, which contain as an active ingredient one or more Licensed Compounds.

     1.22 "Material(s)" shall mean any chemical or biological materials, other
than Licensed Compound(s) and Licensed Product(s), relating (i) to VLA-4 or
VLA-4 Compounds, [*] discovered and/or developed by or on behalf of TBC and/or
any of its Affiliates prior to the Effective Date "[*] or by or on behalf of
TBC and/or any of its Affiliates during the Research Term and in performance of
the Research Program.

     1.23 "NDA" shall mean a New Drug Application, Product License Application
or its equivalent filed with the United States Food and Drug Administration
seeking approval to market and sell a Licensed Product in the United States.

     1.24 "Net Sales" shall mean, with respect to each country in the
Territory, amounts actually received on sales by Schering, its Affiliates or
sublicensees on all sales of Licensed Product to an unaffiliated third party
(whether an end-user, a distributor or otherwise), "[*]

     1.25 [*]

     1.26 "Proprietary Information" shall mean, as applicable, all Schering
Know-How, VLA-4 Know-How, "[*] and all other scientific, clinical, regulatory,
marketing, financial and

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


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commercial information or data, whether communicated in writing, verbally or
electronically, which is provided by one party to the other party in connection
with this Agreement.

     1.27 "Regulatory Approval" shall mean any applications or approvals,
including any INDs, NDAs, HRDs, supplements, amendments, pre- and
post-approvals, marketing authorizations based upon such approvals (including
any prerequisite manufacturing approvals or authorizations related thereto) and
pricing, third party reimbursement or labeling approval(s), technical, medical
and scientific licenses, registrations or authorizations of any national,
supra-national (e.g. the European Commission, the Council of the European
Union, or the European Agency for the Evaluation of Medicinal Products),
regional, state or local regulatory agency, department, bureau, commission,
council or other governmental entity, necessary for the manufacture,
distribution, use, import, export or sale of Licensed Product(s) and/or
Licensed Compound(s) in the Territory.

     1.28 [*]

     1.29 "Research Inventions" shall have the meaning set forth in Section 2.6
hereof.

     1.30 "Research Plan" shall mean the research plan which is attached hereto
as Schedule 1.30 and herein incorporated by reference, including as it may be
amended from time to time during the Research Term upon the mutual written
agreement of the parties.

     1.31 "Research Program" means the research effort to identify and develop
VLA-4 Compounds which is to be conducted by TBC as described in the Research
Plan.

     1.32 "Research Term" shall mean the Initial Research Term and the Extended
Research Term, if any, as set forth in Section 2.8 hereof.

     1.33 "Schering Know-How" shall mean any information, know-how or
materials: (i) owned or controlled by Schering and/or any of its Affiliates as
of the Effective Date relating to VLA-4 Compounds or derivatives thereof; (ii)
discovered or developed by or on behalf of Schering and/or any of its
Affiliates during the term of this Agreement; or (iii) owned or controlled by
Schering and/or any of its Affiliates relating to the development, manufacture,
marketing, use or sale of Licensed Compound(s) and/or Licensed Product(s), and
in each case which during the term of this Agreement are not generally known.
Schering Know-How shall include, without limitation, all applications,
registrations, licenses, authorizations, approvals and correspondence related
to Licensed Compound(s) and/or Licensed Product(s) submitted by Schering to
regulatory authorities as well as all biological, chemical, pharmacological,
toxicological, pharmaceutical, physical and analytical, clinical, safety,
manufacturing and quality control data and information related thereto.

     1.34 "TBC Invention" shall have the meaning set forth in Section 2.6.1.34

     1.35 "Territory" shall mean "[*].

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    a request for confidential treatment filed with the Commission.


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     1.36 "Valid Claim" means a composition-of-matter or method-of-use claim of
an issued and unexpired patent included within the VLA-4 Patent Rights, which
has not been revoked or held unenforceable or invalid by a decision of a court
or other governmental agency of competent jurisdiction, unappealable or
unappealed within the time allowed for appeal, and which has not been
disclaimed, denied or admitted to be invalid or unenforceable through reissue
or disclaimer or otherwise.

     1.37 "VLA-4" means the alpha-4-beta-1 integrin receptor subtype.

     1.38 "VLA-4 Compound" shall mean "[*]

     1.39 "VLA-4 Know-How" shall mean any information, know-how or materials:
(i) owned or controlled by TBC and/or any of its Affiliates as of the Effective
Date relating to VLA-4; (ii) discovered or developed by or on behalf of TBC
and/or any of its Affiliates during the term of this Agreement in performance
of the Research Program; or (iii) owned or controlled by TBC and/or any of its
Affiliates relating to the research, development, manufacture, marketing, use
or sale of Licensed Compound(s) and/or Licensed Product(s), and in each case
which are not in the public domain. VLA-4 Know-How shall include, without
limitation, all applications, registrations, licenses, authorizations,
approvals and correspondence relating to Licensed Compound(s) and/or Licensed
Product(s) submitted by TBC to regulatory authorities as well as all
biological, chemical, pharmacological, toxicological, pharmaceutical, physical
and analytical, clinical, safety, manufacturing and quality control data and
information related thereto.

     1.40 "VLA-4 Patent Rights" shall mean any and all patents and patent
applications (which for the purposes of this Agreement shall be deemed to
include certificates of invention and applications for certificates of
invention) which during the term of this Agreement are owned by TBC (and/or any
of its Affiliates), or to which TBC (and/or any of its Affiliates) through
license or otherwise acquires rights, including, but not limited to, those
listed in Schedule 1.40, which (A) have claims covering: (i) Material or
methods for the preparation or use thereof; (ii) VLA-4 Compound or the
manufacture and/or use thereof, (iii) Licensed Product containing a VLA-4
Compound or the manufacture and/or use thereof, or (iv) subject matter which is
or relates to Research Inventions; (B) are substitutions, divisions,
continuations, continuations-in-part, reissues, renewals, registrations,
confirmations, re-examinations, extensions, supplementary protection
certificates or the like, or the provisional applications of any such patents
and patent applications; or (C) are foreign equivalents of any of the above.

                         ARTICLE II - RESEARCH PROGRAM

     2.1 General TBC shall engage in the Research Program upon the terms and
conditions set forth in this Agreement, including any applicable Schedules or
Exhibits attached hereto. The activities to be undertaken in the course of
Research Program are set forth in the Research Plan.

     2.2 Performance of Research Program


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     (a) Conduct of Research TBC shall conduct the Research Program in good
scientific manner, and in compliance, in all material respects, with all
material requirements of applicable laws, rules and regulations and all
applicable Good Laboratory Practices to attempt to achieve its objectives
efficiently and expeditiously. TBC shall proceed diligently with the work
contemplated under this Agreement, including, without limitation, as set forth
in the Research Plan, by using good faith efforts to provide, among others, the
following resources:

          (i) [*]; and

         (ii) [*].

         While TBC agrees to proceed diligently with the work contemplated
under this Agreement, neither TBC nor Schering warrants or guarantees that
their efforts will result in a marketable or approvable Development Candidate,
Licensed Compound or Licensed Product, or that the goals specified in the
Research Plan will be achieved within the periods set forth therein.

     (b) Research Effort During the Research Term, including as it may be
extended, TBC shall maintain its activities in performance of the Research
Program at a level appropriate for completion of the Research Program during
the Research Term. [*]

     (c) Personnel [*]

     2.3 Research Committee [*]

     (a) [*]

     (b) [*]

     (c) [*]

     (d) [*]

     2.4 Know-How Disclosures As soon as practicable after the Effective Date,
TBC shall disclose to Schering in writing all VLA-4 Know-How [*] not previously
disclosed to Schering. During the term of the Research Program, TBC shall also
promptly disclose to Schering in writing on an ongoing basis all VLA-4 Know-How
as it is developed, and, if requested in writing by Schering, copies of the
records described in Section 2.5. [*]

     2.5 Records and Reports

     (a) Record Keeping TBC shall maintain records, in sufficient detail and in
good scientific manner appropriate for patent and regulatory purposes, which
shall be complete and accurate in all material respects and shall fully and
properly reflect all work done and results achieved in the performance of the
Research Program. Such records shall include books, records, reports, research
notes, charts, graphs, comments, computations, analyses, recordings,

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    a request for confidential treatment filed with the Commission.


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photographs, computer programs and documentation thereof, computer information
storage media, samples of materials and other graphic or written data generated
in connection with the Research Program, including any data required to be
maintained pursuant to all requirements of applicable laws, rules and
regulations.

     (b) Copies and Inspection of Records During the term of the Research
Program, upon reasonable notice and during normal business hours, TBC shall
permit representatives of Schering to visit TBC's premises and view Research
Program work in progress. TBC shall also permit Schering to review any data or
documentation arising out of or relating to the Research Program and any VLA-4
Know-How. Promptly upon request, TBC shall provide to Schering copies of the
records described in Section 2.5(a).

     2.6 Research Inventions The entire right, title and interest in all
discoveries, Improvements, processes, formulas, data, inventions, know-how and
trade secrets, whether or not patentable, and any patent applications or patents
based thereon in the Territory, relating to Materials, Licensed Compound(s)
and/or Licensed Product(s) and which are made, conceived or reduced to practice:

     (i) solely by employees or agents of TBC (or its Affiliate) shall be owned
solely by TBC ("TBC Inventions");

     (ii) solely by employees or agents of Schering (or its Affiliate) shall be
owned solely by Schering ("Schering Inventions"); and

     (iii) jointly by employees or agents of TBC and employees or agents of
Schering (or their respective Affiliates) shall be owned jointly by TBC and
Schering ("Joint Inventions"). TBC Inventions and Joint Inventions shall
hereinafter be referred to collectively as "Research Inventions".

     2.7 License of Research Inventions

     (a) [*]

     (b) [*]

     2.8 Research Term The term of the Research Program shall commence on the
Effective Date [*].

     2.9 Termination of Research Program [*]

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                             ARTICLE III - LICENSE

     3.1 License Grant

     (a) VLA-4 License Grant TBC hereby grants to Schering an exclusive license
in the Territory in the Field under the VLA-4 Patent Rights and to use the
VLA-4 Know-How to discover, develop, make, have made, import, export, use,
manufacture, have manufactured, distribute, market, promote, offer for sale and
sell Licensed Compound(s) and/or Licensed Product(s). TBC shall retain the
right to use the VLA-4 Patent Rights and VLA-4 Know-How solely in connection
with the Research Program. [*]

     (b) VLA-4 Non-Exclusive License Grant In the event that the discovery,
development, making, having made, importing, exporting, use, manufacturing,
having manufactured, distribution, marketing, promotion, offering for sale or
sale by Schering, its Affiliates and/or sublicensees of Licensed Compound(s)
and/or Licensed Product(s) would, during the term of this Agreement, infringe a
claim of an issued letters patent, or any other patent rights which TBC owns or
has the rights to license and which patents are not covered by the grant in
Section 3.1(a), TBC hereby grants to Schering, to the extent TBC is legally
able to do so, a non-exclusive, [*], license in the Territory under such
issued letters patent solely for Schering to discover, develop, make, have
made, import, export, use, manufacture, have manufactured, distribute, market,
promote, offer for sale and sell Licensed Compound(s) and/or Licensed
Product(s) in the Territory. [*]

     3.2 Right to Sublicense [*]

     3.3 License to TBC In the event that Schering provides Schering Know-How
to TBC, Schering shall grant to TBC the right to use such Schering Know-How in
performance of the Research Program; provided, however, that Schering is not
and shall not be obligated to provide Schering Know-How to TBC.

     3.4 Restriction on Disposition of Licensed Compound TBC and its Affiliates
shall not, during the term of this Agreement make or use any Licensed Compound,
except in connection with the Research Program, or knowingly provide any such
Licensed Compound, for any purpose to any third person or entity.

     3.5 Option to [*]

     (a) [*]

     (b) [*]

     (c) [*]

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.

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                ARTICLE IV - DEVELOPMENT AND COMMERCIALIZATION

     4.1 [*]

     (a) [*]

     (b) [*]

     4.2 [*]

     4.3 Discontinuance of Development

     (a) [*]

     (b) [*]

     4.4 [*]

     4.5 Provision of Information In addition to the obligations set forth in
Section 2.4, following the expiration of the Research Term and until the
termination of this Agreement, TBC shall promptly disclose to Schering in
writing all VLA-4 Know-How developed or acquired by or on behalf of TBC (or its
Affiliates). Such VLA-4 Know-How and other information shall be automatically
deemed to be within the scope of the licenses granted herein without payment of
any additional compensation.

     4.6 [*]"

     4.7 [*]

                  ARTICLE V - PAYMENTS; ROYALTIES AND REPORTS

     5.1 Additional Payment Obligations The parties acknowledge that Schering's
payment obligations as set forth in Sections 5.2, 5.3, 5.4, 5.5 and 5.6 of this
Agreement are in addition to the payment obligations of SP Ltd. set forth in
Section 5.2, 5.3, 5.4, 5.5 and 5.6 of the International Agreement.

     5.2 Research Program Funding In consideration for TBC's performance of its
obligations under the Research Program, Schering shall pay to TBC research
funding at the rate of [*].

     5.3 Consideration for License In consideration for the licenses granted to
Schering hereunder, Schering shall pay to TBC a license fee of [*].

     5.4 Milestone Payments Subject to the terms and conditions of this
Agreement and in consideration for the ongoing provision of data, information
and know-how, Schering shall pay

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to TBC the following payments based on attainment of the research and
development milestones indicated:

         [*]

         Schering shall notify TBC in writing within thirty (30) calendar days
upon the achievement of each milestone, such notice to be accompanied by
payment of the appropriate milestone payment. The applicable milestone payment
shall be payable only upon the initial achievement of such milestone and no
amounts shall be due hereunder for subsequent or repeated achievement of such
milestone.

     5.5 [*]

     5.6 Royalties

     (a) Royalty Rates Subject to the terms and conditions of this Agreement,
Schering shall pay to TBC royalties [*]in an amount equal to:

     [*]

     The parties acknowledge and agree that for purposes of this Agreement
worldwide annual Net Sales shall be determined by [*]

     (b) Term of Royalty Obligation [*]

     (c) Third Party Licenses [*]

     (d) Royalties for Bulk Compound [*]

     5.7 Reports; Payment of Royalty; Payment Exchange Rate and Currency
Conversions

     (a) [*]

     (b) Method of Payment [*]

     5.8 Maintenance of Records; Audits

     (a) Record keeping by Schering Schering and its Affiliates shall keep
complete and accurate records in sufficient detail to enable the royalties
payable hereunder to be determined. [*].

     (b) Underpayments/Overpayments [*]

     (c) Record Keeping by Sublicensee Schering shall include in each
sublicense granted by it pursuant to this Agreement a provision requiring the
sublicensee to make reports to

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                                      10

<PAGE>   16

Schering, to keep and maintain records of sales made pursuant to such
sublicense and to grant access to such records by TBC's independent accountant
[*].

     (d) Confidentiality TBC shall treat all financial information subject to
review under this Section 5.8, or under any sublicense agreement, in accordance
with the confidentiality provisions of Article VII of this Agreement, [*]

     5.9 Income Tax Withholding If at any time, any jurisdiction within the
Territory requires the withholding of income taxes or other taxes imposed upon
payments set forth in this Article V, [*].

     5.10 Direct Affiliate Licenses [*]

     5.11 Animal Health Indications In the event that Schering and/or its
Affiliates develop a Licensed Compound or Licensed Product for any animal
health indication, the parties will negotiate, in good faith, reduced
milestones and royalty terms appropriate for such animal health product.

                             ARTICLE VI - PATENTS

     6.1 Filing, Prosecution and Maintenance of Patents [*]

     6.2 "[*]

     6.3 Enforcement

     (a) Notice and Discontinuance of Infringement In the event that either
Schering or TBC becomes aware of any alleged or threatened infringement in a
country in the Territory of any issued patent within the VLA-4 Patent Rights,
it will notify the other party in writing to that effect. [*]

     (b) Continuance of Infringement [*]

     6.4 Infringement and Third Party Licenses

     (a) Course of Action [*]

     (b) [*]

     (c) [*]

     6.5 Third Party Infringement Suit [*]

     6.6 Abandonment [*]

     6.7 Patent Term Restoration [*]

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                                      11

<PAGE>   17

     6.8 Notices Regarding Patents All notices, inquiries and communications
made in connection with this Article VI shall be sent in the manner set forth
in Section 11.7 to the parties at the addresses and facsimile numbers indicated
below.

         If to TBC:

                  Texas Biotechnology Corporation
                  7000 Fannin, 20th floor
                  Houston, TX  77030
                  Attn:  President

                  with a copy to:

                  Porter & Hedges, L.L.P.
                  700 Louisiana, 35th Floor
                  Houston, TX  77002-2764
                  Attn:  Robert G. Reedy

         If to Schering:

                  Schering Corporation
                  2000 Galloping Hill Road
                  Kenilworth, New Jersey  07033
                  Attn: Staff Vice President - Patents and Trademarks
                  Fax No.: 908  298-5388


                 ARTICLE VII - CONFIDENTIALITY AND PUBLICATION

     7.1 Confidentiality

     (a) Nondisclosure Obligation Each of TBC and Schering shall use any
Proprietary Information received by it from the other party only in accordance
with this Agreement and shall not disclose to any third party any such
Proprietary Information without the prior written consent of the other party.
The foregoing obligations shall survive the expiration or termination of this
Agreement for a period of ten (10) years. These obligations shall not apply to
Proprietary Information that:

     (i) is known by the receiving party at the time of its receipt, and not
through a prior disclosure by the disclosing party, as documented by business
records;

     (ii) is at the time of disclosure, or thereafter becomes, published or
otherwise part of the public domain without breach of this Agreement by the
receiving party;

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                                      12

<PAGE>   18

     (iii) is subsequently disclosed to the receiving party by a third party
who has the right to make such disclosure;

     (iv) is independently developed by the receiving party or its Affiliates
outside of the Research Program and without use of the disclosing party's
Proprietary Information, and such independent development can be documented by
the receiving party;

     (v) is disclosed to any institutional review board of any entity
conducting clinical trials with Licensed Compound(s) or Licensed Product(s) or
to any governmental or other regulatory agencies in order to obtain patents or
to gain approval to conduct clinical trials or to market Licensed Compound
and/or Licensed Product, provided that such disclosure may be made only to the
extent reasonably necessary to obtain such patents or authorizations; or

     (vi) is required to be disclosed by law, regulation, rule, act or order of
any governmental authority or agency to be disclosed, provided that notice is
promptly delivered to the other party in order to provide an opportunity to
seek a protective order or other similar order with respect to such Proprietary
Information and thereafter the receiving party discloses to the requesting
entity only the minimum information required to be disclosed in order to comply
with the request, whether or not a protective order or other similar order is
obtained by the other party.

     (b) Disclosure to Agents Notwithstanding the provisions of Section 7.1(a)
and subject to the other terms of this Agreement, each of Schering and TBC
shall have the right to disclose Proprietary Information to their respective
sublicensees, agents, consultants, Affiliates or other third parties
(collectively "Agents") in accordance with this Section 7.1(b). Such disclosure
shall be limited only to those Agents directly involved in the research,
development, manufacturing, marketing or promotion of Licensed Compound or
Licensed Product (or for such Agents to determine their interest in performing
such activities) in accordance with this Agreement. Any such Agents must agree
in writing to be bound by confidentiality and non-use obligations essentially
the same as those contained in this Agreement. [*]

     7.2 Return of Confidential Information Upon termination of this Agreement,
the receiving party will return all documents, and copies thereof, including
those in the possession of the receiving party's Agents pursuant to Section
7.1(b), containing the disclosing party's Proprietary Information at any time
upon request of the disclosing party. However, the receiving party may retain
one copy of such documents in a secure location solely for the purposes of (i)
determining its obligations hereunder, (ii) complying with any applicable
regulatory requirements, or (iii) defending against any product liability
claim.

     7.3 No Publicity A party may not use the name of the other party in any
publicity or advertising and may not issue a press release or otherwise
publicize or disclose any information related to the existence of this
Agreement or the terms or conditions hereof, except (i) on the advice of its
counsel as required by law (e.g., any Securities and Exchange Commission
filings and disclosures) and provided the party who will be disclosing such
information has consulted with the other party to the extent feasible prior to
such disclosure with respect to the substance of

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                                      13

<PAGE>   19
the disclosure; or (ii) as consented to in advance by the other party in
writing. The parties shall agree on a form of initial press release that may be
used by either party on an ongoing basis to describe this Agreement.

     7.4 Publication Each of Schering and TBC acknowledges the other party's
interest in publishing its results to obtain recognition within the scientific
community and to advance the state of scientific knowledge. Each party also
recognizes the mutual interest in obtaining valid patent protection and in
protecting business interests and trade secret information. [*]

                 ARTICLE VIII - REPRESENTATIONS AND WARRANTIES

     8.1 Representations and Warranties of Each Party Each of TBC and Schering
hereby represents, warrants and covenants to the other party hereto as follows:

     (a) it is a corporation duly organized and validly existing under the laws
of the state or other jurisdiction of its incorporation;

     (b) the execution, delivery and performance of this Agreement by such
party has been duly authorized by all requisite corporate action, subject only
to receipt of requisite boards of directors' approvals;

     (c) it has the power and authority to execute and deliver this Agreement
and to perform its obligations hereunder;

     (d) the execution, delivery and performance by such party of this
Agreement and its compliance with the terms and provisions hereof does not and
will not conflict with or result in a breach of any of the terms and provisions
of or constitute a default under (i) a loan agreement, guaranty, financing
agreement, agreement affecting a product or other agreement or instrument
binding or affecting it or its property; (ii) the provisions of its corporate
charter or other operative documents or bylaws; or (iii) any order, writ,
injunction or decree of any court or governmental authority entered against it
or by which any of its property is bound;

     (e) except for the governmental and Regulatory Approvals required to
market the Licensed Product in the Territory, the execution, delivery and
performance of this Agreement by such party does not require the consent,
approval or authorization of, or notice, declaration, filing or registration
with, any governmental or regulatory authority and the execution, delivery or
performance of this Agreement will not violate any law, rule or regulation
applicable to such party;

     (f) this Agreement has been duly authorized, executed and delivered and
constitutes such party's legal, valid and binding obligation enforceable
against it in accordance with its terms subject, as to enforcement, to
bankruptcy, insolvency, reorganization and other laws of general applicability
relating to or affecting creditors' rights and to the availability of
particular remedies under general equity principles; and

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                                      14

<PAGE>   20

     (g) it shall comply with all applicable material laws and regulations
relating to its activities under this Agreement.

     8.2 TBC's Representations TBC hereby represents, warrants and covenants to
Schering as follows:

     (a) to the best of TBC's knowledge, as of the Effective Date the VLA-4
Patent Rights and VLA-4 Know-How are subsisting and are not invalid or
unenforceable, in whole or in part;

     (b) as of the Effective Date it has the full right, power and authority to
grant all of the right, title and interest in the licenses and options granted
under Article III hereof;

     (c) as of the Effective Date it has not assigned, transferred, conveyed or
otherwise encumbered, and during the term of this Agreement will not assign,
transfer, convey of otherwise encumber, its right, title and interest in the
VLA-4 Patent Rights or VLA-4 Know-How (except in accordance with this
Agreement);

     (d) to the best of TBC's knowledge, as of the Effective Date it is the
sole and exclusive owner of the VLA-4 Patent Rights and VLA-4 Know-How, all of
which is free and clear of any liens, charges and encumbrances, and no other
person, corporate or other private entity, or governmental entity or
subdivision thereof, has or shall have any claim of ownership with respect to
the VLA-4 Patent Rights and VLA-4 Know-How, whatsoever;

     (e) during the term of this Agreement, TBC shall not take any action which
would (i) create any liens, charges or encumbrances with respect to the VLA-4
Patent Rights, VLA-4 Know-How [*] whatsoever, or (ii) give rise to any third
party claim of ownership with respect to the VLA-4 Patent Rights, VLA-4 Know-How
[*] whatsoever;

     (f) to the best of TBC's knowledge, as of the Effective Date the licensed
VLA-4 Patent Rights and VLA-4 Know-How, and the development, manufacture, use,
distribution, marketing, promotion and sale of Licensed Compound and Licensed
Products do not interfere or infringe on any intellectual property rights owned
or possessed by any third party;

     (g) to the best of TBC's knowledge, except for the [*], as of the
Effective Date there are no third party pending patent applications which, if
issued, may cover the development, manufacture, use, distribution, marketing,
promotion or sale of Licensed Compounds or Licensed Products;

     (h) as of the Effective Date there are no claims, judgments or settlements
against or owed by TBC or pending or threatened claims or litigation against
TBC relating to VLA-4 Patent Rights and VLA-4 Know-How;

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                                      15

<PAGE>   21
     (i) it has disclosed to Schering all VLA-4 Know-How, [*], and other
relevant information required to be disclosed hereunder, including, without
limitation, information relating to the VLA-4 Patent Rights, Materials, [*]
VLA-4 Compounds and the Research Program;

     (j) as of the Effective Date, it is in compliance in all material respects
with any agreements with third parties and during the term of this Agreement
(i) it will use diligent efforts not to diminish the rights under the VLA-4
Patent Rights and VLA-4 Know-How granted to Schering hereunder, including
without limitation, by not committing or permitting any actions or omissions
which would cause the breach of any agreements between itself and third parties
which provide for intellectual property rights applicable to the development,
manufacture, use, distribution, marketing, promotion or sale of Licensed
Compounds and/or Licensed Products, and (ii) it will provide Schering promptly
with notice of any such alleged breach; and

     (k) during the term of this Agreement it will not use in any capacity, in
connection with any services to be performed under this Agreement, any
individual who has been debarred pursuant to the United States Food, Drug and
Cosmetic Act.

     8.3  Schering's Representations Schering hereby represents, warrants and
covenants to TBC as follows:

     (a) during the term of this Agreement it will not use in any capacity, in
connection with any services to be performed under this Agreement, any
individual who has been debarred pursuant to the United States Food, Drug and
Cosmetic Act;

     (b) to the best of Schering's knowledge, as of the Effective Date it is
the sole and exclusive owner of the Schering Know-How, all of which is free and
clear of any liens, charges and encumbrances, and no other person, corporate or
other private entity, or governmental entity or subdivision thereof, has or
shall have any claim of ownership with respect to the Schering Know-How,
whatsoever; and

     (c) as of the Effective Date, it is in compliance in all material respects
with any agreements with third parties and during the term of this Agreement
(i) it will use diligent efforts not to diminish the rights under the Schering
Know-How granted to TBC hereunder, including without limitation, by not
committing or permitting any actions or omissions which would cause the breach
of any agreements between itself and third parties which provide for
intellectual property rights applicable to the development, manufacture, use or
sale of Licensed Compounds and/or Licensed Products, and (ii) it will provide
TBC promptly with notice of any such alleged breach.

     8.4 No Inconsistent Agreements Neither party has in effect, and after the
Effective Date neither party shall enter into, any oral or written agreement or
arrangement that would be inconsistent with its obligations under this
Agreement.

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<PAGE>   22

     8.5 Representation by Legal Counsel Each party hereto represents that it
has been represented by legal counsel in connection with this Agreement and
acknowledges that it has participated in the drafting hereof. In interpreting
and applying the terms and provisions of this Agreement, the parties agree that
no presumption shall exist or be implied against the party which drafted such
terms and provisions.

           ARTICLE IX - INDEMNIFICATION AND LIMITATION ON LIABILITY

     9.1 Indemnification by Schering Schering shall indemnify, defend and hold
harmless TBC and its Affiliates, and each of its and their respective
employees, officers, directors and agents (each, a "TBC Indemnified Party")
from and against any and all liability, loss, damage, cost, and expense
(including reasonable attorneys' fees), subject to the limitations in Section
9.5 (collectively, a "Liability") which a TBC Indemnified Party may incur,
suffer or be required to pay resulting from or arising out of (i) the
development, manufacture, promotion, distribution, use, marketing, sale or
other disposition of Licensed Compounds and/or Licensed Products by Schering,
its Affiliates or sublicensees, and (ii) any breach by Schering of any of its
representations, warranties and covenants contained in Sections 8.1 and 8.3
hereof. Notwithstanding the foregoing, Schering shall have no obligation under
this Agreement to indemnify, defend or hold harmless any TBC Indemnified Party
with respect to claims, demands, costs or judgments which result from the gross
negligence or willful misconduct of TBC, its Affiliates, or any of their
respective employees, officers, directors or agents.

     9.2 Indemnification by TBC TBC shall indemnify, defend and hold harmless
Schering and its Affiliates, and each of its and their respective employees,
officers, directors and agents (each, a "Schering Indemnified Party") from and
against any Liability which a Schering Indemnified Party may incur, suffer or
be required to pay resulting from or arising in connection with (i) the
performance of the Research Program by TBC, its Affiliates, or any of their
respective employees, officers, directors or agents, and (ii) any breach by TBC
of any of its representations, warranties and covenants contained in Sections
8.1 and 8.2 hereof.

     9.3 Conditions to Indemnification The obligations of the indemnifying
party under Sections 9.1 and 9.2 are conditioned upon the delivery of written
notice to the indemnifying party of any potential Liability promptly after the
indemnified party becomes aware of such potential Liability. The indemnifying
party shall have the right to assume the defense of any suit or claim related
to the Liability if it has assumed responsibility for the suit or claim in
writing; however, if in the reasonable judgment of the indemnified party, such
suit or claim involves an issue or matter which could have a materially adverse
effect on the business operations or assets of the indemnified party, the
indemnified party may retain control of the defense or settlement thereof by
providing written notice of such effect to the indemnifying party, but in no
event shall such action or notice be construed as a waiver of any
indemnification rights that the indemnified party may have at law or in equity.
If the indemnifying party defends the suit or claim, the indemnified party may
participate in (but not control) the defense thereof at its sole cost and
expense. The foregoing notwithstanding, the parties acknowledge and agree that
failure of the indemnified party to promptly notify the indemnifying party of a
potential Liability shall not constitute a

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                                      17

<PAGE>   23

waiver of, or result in the loss of, such party's right to indemnification
under Section 9.1 or 9.2, as appropriate, except to the extent that the
indemnifying party's rights, and/or its ability to defend against such
Liability, are materially prejudiced by such failure to notify.

     9.4 Settlements Neither party may settle a claim or action related to a
Liability without the consent of the other party, which consent shall not be
unreasonably withheld, if such settlement would impose any monetary obligation
on the other party or require the other party to submit to an injunction or
otherwise limit the other party's rights under this Agreement. Any payment made
by a party to settle any such claim or action shall be at its own cost and
expense.

     9.5 Limitation of Liability With respect to any claim by one party against
the other arising out of the performance or failure of performance of the other
party under this Agreement, the parties expressly agree that the liability of
such party to the other party for such breach shall be limited under this
Agreement or otherwise at law or equity to direct damages only and in no event
shall a party be liable for punitive, exemplary or consequential damages.

     9.6 Insurance Each party acknowledges and agrees that during the term of
this Agreement it shall maintain adequate insurance and/or a self-insurance
program for liability insurance, including products liability and contractual
liability insurance, to cover such party's obligations under this Agreement.
Each party shall provide the other party with evidence of such insurance and/or
self-insurance program, upon request.

                       ARTICLE X - TERM AND TERMINATION

     10.1 Term and Expiration This Agreement shall be effective as of the
Effective Date and unless terminated earlier by mutual written agreement of the
parties or pursuant to Sections 10.2 or 10.3 below, the term of this Agreement
shall continue in effect [*] until the earlier to occur of (i) expiration of
Schering's obligation to pay royalties under Article V hereof, or (ii) the
thirtieth (30th) anniversary of the Effective Date. [*]

     10.2 Termination by Schering

     (a)  Schering's Right to Terminate Notwithstanding anything contained
herein to the contrary, Schering shall have the unilateral right to terminate
this Agreement, with or without cause, at any time by giving one hundred eighty
(180) days advance written notice to TBC. In the event of such termination, the
rights and obligations hereunder shall terminate; provided, however, that any
payment obligations due and owing as of the termination date shall continue.

     (b) Effect of Termination Notwithstanding anything contained herein to the
contrary, following any termination under Section 10.2(a), [*]

     10.3 Termination

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<PAGE>   24

     (a) Termination for Cause This Agreement may be terminated by notice by
either party at any time during the term of this Agreement:

     (i) if the other party is in breach of its material obligations hereunder
and has not cured such breach within ninety (90) days after notice requesting
cure of the breach, or in the event that the breach cannot be reasonably cured
within such ninety (90) day period, has not initiated actions reasonably
expected to cure such breach within ninety (90) days after receipt of notice
and thereafter diligently pursues such actions to cure the breach; or

     (ii) upon the filing or institution of bankruptcy, reorganization,
liquidation or receivership proceedings, or upon an assignment of a substantial
portion of the assets for the benefit of creditors by the other party, or in
the event a receiver or custodian is appointed for such party's business, or if
a substantial portion of such party's business is subject to attachment or
similar process; provided, however, that in the case of any involuntary
bankruptcy proceeding such right to terminate shall only become effective if
the proceeding is not dismissed within sixty (60) days after the filing
thereof.

     (b) Effect of Termination for Cause on License

     (i) Termination for Breach or Change of Control In the event Schering
terminates this Agreement under Sections 10.3(a)(i) or 11.1(c), Schering's
licenses pursuant to Sections 3.1 and 3.2 shall become fully paid-up, perpetual
licenses.

     (ii) Termination for Diligence Failure In the event that TBC terminates
this Agreement under Sections 4.1(b) and/or 10.3(a)(i), then the rights and
licenses granted to Schering under Sections 3.1 and 3.2 of this Agreement shall
terminate and all rights to Licensed Compounds and Licensed Products shall
revert to TBC. In the event of such termination by TBC, Schering shall grant to
TBC a license to use Schering Know-How necessary to develop, make, have made,
use and sell Licensed Compounds or Licensed Products to which TBC holds rights
hereunder; provided, however, in the event that TBC successfully develops
Licensed Compounds or Licensed Products then TBC shall promptly notify Schering
to that effect. Schering shall thereafter have an exclusive option to negotiate
an exclusive license for commercial purposes to such Licensed Compounds or
Licensed Products. Schering shall exercise such option by advising TBC, in
writing, of its interest in obtaining an exclusive license to any development.
Schering shall exercise its option and negotiate such license agreement within
six (6) months of Schering's receipt of notice of said development. If Schering
exercises its option and the parties fail, in good faith, to execute a mutually
acceptable license agreement within such six (6) month period, TBC will be free
to license its interests in the development to any third party.

     (iii) Effect of Bankruptcy In the event Schering terminates this Agreement
under Sections 10.3(a)(ii) or this Agreement is otherwise terminated under
Section 10.3(a)(ii), the parties agree that Schering, as a licensee of rights
to intellectual property under this Agreement,

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<PAGE>   25

shall retain and may fully exercise all of its rights and elections under Title
11, including as set forth in Section 11.8 hereof.

     10.4 Effect of Termination Termination of this Agreement by either party
pursuant to Section 10.1, 10.2 or 10.3 hereof shall constitute termination of
the International Agreement under the corresponding provisions thereof.
Expiration or termination of the Agreement shall not relieve the parties of any
obligation accruing prior to such expiration or termination, and the provisions
of Sections 2.5, 3.4, 4.7, and Articles VII and IX shall survive the expiration
of the Agreement. Any expiration or early termination of this Agreement shall
be without prejudice to the rights of either party against the other accrued or
accruing under this Agreement prior to termination, including the obligation to
pay royalties for Licensed Product(s) or Compound sold prior to such
termination.

     10.5 Effect of New Developments[*]

                          ARTICLE XI - MISCELLANEOUS

     11.1 Assignment/Change of Control

     (a) [*]
     (b) [*]
     (c) [*]
     (d) [*]

     (e) Definition of Change of Control. As used in this Section 11.1 the term
"Change of Control" shall mean (i) any merger, reorganization, consolidation or
combination in which a party to this Agreement is not the surviving
corporation, or (ii) any "person" (within the meaning of Sections 13(d) and 14
(d)(2) of the Securities Exchange Act of 1934), excluding Schering and its
Affiliates, is or becomes the beneficial owner, directly or indirectly, of
securities of the party representing 50% or more of either (a) the
then-outstanding shares of common stock of the party or its parent corporation,
or (b) the combined voting power of the party's then-outstanding voting
securities; or (iii) if individuals who as of the Effective Date constitute the
Board of Directors of the party or its parent corporation (the "Incumbent
Board") cease for any reason to constitute at least a majority of such Board of
Directors; provided, however, that any individual becoming a director
subsequent to the Effective Date whose election, or nomination for election by
the party's shareholders, was approved by a vote of at least a majority of the
directors then comprising the Incumbent Board shall be considered as though
such individual were a member of the Incumbent Board, but excluding, for this
purpose, any such individual whose initial

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<PAGE>   26

assumption of office occurs as a result of an actual or threatened election
contest with respect to the election or removal of directors or other actual or
threatened solicitation of proxies or consents by or on behalf of a person
other than the Incumbent Board; or (iv) approval by the shareholders of a party
of a complete liquidation or the complete dissolution of such party.

     11.2 Governing Law This Agreement shall be governed, interpreted and
construed in accordance with the laws of the State of Delaware, without giving
effect to its conflict of law principles. The parties expressly exclude
application of the United Nations Convention for the International Sale of
Goods. [*]

     11.3 Waiver Any delay or failure in enforcing a party's rights under this
Agreement or any waiver as to a particular default or other matter shall not
constitute a waiver of such party's rights to the future enforcement of its
rights under this Agreement, nor operate to bar the exercise or enforcement
thereof at any time or times thereafter, excepting only as to an express
written and signed waiver as to a particular matter for a particular period of
time.

     11.4 Independent Relationship Nothing herein contained shall be deemed to
create an employment, agency, joint venture or partnership relationship between
the parties hereto or any of their agents or employees, or any other legal
arrangement that would impose liability upon one party for the act or failure
to act of the other party. Neither party shall have any power to enter into any
contracts or commitments or to incur any liabilities in the name of, or on
behalf of, the other party, or to bind the other party in any respect
whatsoever.

     11.5 Export Control This Agreement is made subject to any restrictions
concerning the export of products or technical information from the United
States of America which may be imposed upon or related to TBC or Schering from
time to time by the government of the United States of America. Furthermore,
Schering agrees that it will not export, directly or indirectly, any technical
information acquired from TBC under this Agreement or any products using such
technical information to any country for which the United States government or
any agency thereof at the time of export requires an export license or other
governmental approval, without first obtaining the written consent to do so from
the Department of Commerce or other agency of the United States government when
required by an applicable statute or regulation.

     11.6 Entire Agreement; Amendment This Agreement, including the Exhibits
and Schedules hereto and thereto, sets forth the complete, final and exclusive
agreement and all the covenants, promises, agreements, warranties,
representations, conditions and understandings between the parties hereto and
supersedes and terminates all prior agreements and understandings between the
parties with regard to the subject matter hereof in the Territory. There are no
covenants, promises, agreements, warranties, representations, conditions or
understandings, either oral or written, between the parties other than as are
set forth herein and therein. No subsequent alteration, amendment, change,
waiver or addition to this Agreement shall be binding upon the parties unless
reduced to writing and signed by an authorized officer of each party.

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<PAGE>   27

     11.7 Notices Except as provided under Section 6.8 hereof, any notice
required or permitted to be given or sent under this Agreement shall be hand
delivered or sent by express delivery service or certified or registered mail,
postage prepaid, or by facsimile transmission (with written confirmation copy
by registered first-class mail) to the parties at the addresses and facsimile
numbers indicated below.

         If to TBC, to:

         Texas Biotechnology Corporation
         7000 Fannin, 20th floor
         Houston, TX  77030
         Attn:  President

         with a copy to:

         Porter & Hedges, L.L.P.
         700 Louisiana, 35th Floor
         Houston, TX  77002-2764
         Attn:  Robert G. Reedy

         If to Schering, to:

         Schering Corporation
         2000 Galloping Hill Road
         Kenilworth, New Jersey  07033
         Attention: President, Business Development
         Facsimile No.: (908) 298-5379

         and

         Schering Corporation
         2000 Galloping Hill Road
         Kenilworth, New Jersey  07033
         Attention: Law Department - Staff Vice-President, Licensing
         Facsimile No.: (908) 298-2739

         Any such notice shall be deemed to have been received on the earlier
of the date actually received or the date five (5) days after the same was
posted or sent. Either party may change its address or its facsimile number by
giving the other party written notice, delivered in accordance with this
Section 11.7.

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    a request for confidential treatment filed with the Commission.


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<PAGE>   28

     11.8 Provisions for Insolvency

     (a) Effect on Licenses All rights and licenses granted under or pursuant
to this Agreement by TBC to Schering are, for all purposes of Section 365(n) of
Title 11 of the United States Code ("Title 11"), licenses of rights to
"intellectual property" as defined in Title 11. TBC agrees during the term of
this Agreement to create and maintain current copies or, if not amenable to
copying, detailed descriptions or other appropriate embodiments, to the extent
feasible, of all such intellectual property. If a case is commenced by or
against TBC under Title 11, then, unless and until this Agreement is rejected
as provided in Title 11, TBC (in any capacity, including debtor-in-possession)
and its successors and assigns (including, without limitation, a Title 11
Trustee (as defined therein)) shall, as Schering may elect in a written
request, immediately upon such request:

     (i) [*]

     (ii) [*]

     (b) Rights to Intellectual Property If a Title 11 case is commenced by or
against TBC, and this Agreement is rejected as provided in Title 11, and
Schering elects to retain its rights hereunder as provided in Title 11, then
TBC (in any capacity, including debtor-in-possession) and its successors and
assigns (including, without limitation, a Title 11 Trustee) [*].

     (c)  Schering's Rights All rights, powers and remedies of Schering provided
herein are in addition to and not in substitution for any and all other rights,
powers and remedies now or hereafter existing at law or in equity (including,
without limitation, Title 11). In the event of the commencement of a Title 11
case by or against TBC. Schering, in addition to the rights, power and remedies
expressly provided herein, shall be entitled to exercise all other such rights
and powers and resort to all other such remedies as may now or hereafter exist
at law or in equity (including, without limitation, Title 11) in such event. The
parties agree that they intend the foregoing Schering rights to extend to the
maximum extent permitted by law, including, without limitation, for purposes of
Title 11:

     (i) the right of access to any intellectual property (including all
embodiments thereof) of TBC, or any third party with whom TBC contracts to
perform an obligation of TBC under this Agreement, and, in the case of the
third party, which is necessary for the development, registration, manufacture
and marketing of Licensed Compounds and/or Licensed Products; and

     (ii) the right to contract directly with any third party described in (i)
to complete the contracted work.

     (d) Effect on International Agreement The parties acknowledge and agree
that the occurrence of any event or series of events which gives effect to any
of Schering's rights under Sections 11.8(a), 11.8(b) and/or 11.8(c) of this
Agreement shall have the same effect with respect to SP Ltd.'s rights under the
corresponding provisions of the International Agreement.

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    a request for confidential treatment filed with the Commission.


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<PAGE>   29

     11.9 Force Majeure Failure of any party to perform its obligations under
this Agreement (except the obligation to make payments when properly due) shall
not subject such party to any liability or place them in breach of any term or
condition of this Agreement to the other party if such failure is due to any
cause beyond the reasonable control of such non-performing party ("force
majeure"), unless conclusive evidence to the contrary is provided. Causes of
non-performance constituting force majeure shall include, without limitation,
acts of God, fire, explosion, flood, drought, war, riot, sabotage, embargo,
strikes or other labor trouble, failure in whole or in part of suppliers to
deliver on schedule materials, equipment or machinery, interruption of or delay
in transportation, a national health emergency or compliance with any order or
regulation of any government entity acting with color of right. The party
affected shall promptly notify the other party of the condition constituting
force majeure as defined herein and shall exert reasonable efforts to
eliminate, cure and overcome any such causes and to resume performance of its
obligations with all possible speed; provided that nothing herein shall
obligate a party to settle on terms unsatisfactory to such party any strike,
lockout or other labor difficulty, any investigation or other proceeding by any
public authority or any litigation by any third party. If a condition
constituting force majeure as defined herein exists for more than [*]
consecutive days, the parties shall meet to negotiate a mutually satisfactory
resolution to the problem, if practicable. If the parties cannot in good faith
reach a satisfactory resolution to the problem [*].

     11.10 Severability If any provision of this Agreement is declared illegal,
invalid or unenforceable by a court having competent jurisdiction, it is
mutually agreed that this Agreement shall continue in accordance with its terms
except for the part declared invalid or unenforceable by order of such court,
provided, however, that in the event that the terms and conditions of this
Agreement are materially altered, the parties will, in good faith, renegotiate
the terms and conditions of this Agreement to reasonably substitute such
invalid or unenforceable provisions in light of the intent of this Agreement.

     11.11 Counterparts This Agreement shall become binding when any one or
more counterparts hereof, individually or taken together, shall bear the
signatures of each of the parties hereto. This Agreement may be executed in any
number of counterparts, each of which shall be an original as against either
party whose signature appears thereon, but all of which taken together shall
constitute but one and the same instrument.

     11.12 Captions The captions of this Agreement are solely for the
convenience of reference and shall not affect its interpretation.

     11.13 Recording Each party shall have the right, at any time, to record,
register, or otherwise notify this Agreement in appropriate governmental or
regulatory offices anywhere in the world, and each party shall provide
reasonable assistance to the other in effecting such recording, registering or
notifying. The parties acknowledge that this Agreement may be notified to the
European Community for compliance with applicable laws.11.13

     11.14 Further Actions Each party agrees to execute, acknowledge and deliver
such further instruments, and to do all other acts, as may be necessary or
appropriate in order to carry

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    a request for confidential treatment filed with the Commission.


                                      24

<PAGE>   30

out the purposes and intent of this Agreement including, without limitation,
any filings with any antitrust agency which may be required.

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    a request for confidential treatment filed with the Commission.


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<PAGE>   31

     IN WITNESS WHEREOF, this Agreement has been executed by the duly
authorized representatives of the parties as of the date set forth below.

     TEXAS BIOTECHNOLOGY CORPORATION            SCHERING CORPORATION


     By:                                        By:
        -----------------------------               ---------------------------
                                                         Thomas C. Lauda

     Title:                                     Title: Executive Vice President
           --------------------------                  ------------------------

     Date:                                      Date:
          ---------------------------                 -------------------------

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


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