<PAGE>   1
        [Confidential treatment has been requested for portions of this
exhibit.  The confidential portions have been redacted and are denoted by [**]. 
The confidential portions have been separately filed with the Securities and
Exchange Commission.]














                DRUG DEVELOPMENT AND COMMERCIALIZATION AGREEMENT




                                 BY AND BETWEEN




                             THE BURNHAM INSTITUTE




                                      AND




                                 ILEX ONCOLOGY
<PAGE>   2
                               TABLE OF CONTENTS

<TABLE>
<S>                                                                                          <C>
ARTICLE I DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   1
                                                                                        
ARTICLE II LICENSE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
         2.1     License to Technology  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
         2.2     License to Telios Technology . . . . . . . . . . . . . . . . . . . . . . .   7
                                                                                        
ARTICLE III CONSIDERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
         3.1     Earned Royalties . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
         3.2     Accrued Royalties  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
         3.3     Minimum Royalties  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
         3.4     Payment of Minimum Royalties . . . . . . . . . . . . . . . . . . . . . . .   8
         3.5     Stock Warrant  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
         3.6     Milestone Payments . . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
         3.7     License Fee  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
         3.8     Reduction of Royalties . . . . . . . . . . . . . . . . . . . . . . . . . .   9
                                                                                        
ARTICLE IV CLINICAL DEVELOPMENT AND MANUFACTURING . . . . . . . . . . . . . . . . . . . . .  10
         4.1     Clinical Development . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
         4.2     Development Plan Milestones  . . . . . . . . . . . . . . . . . . . . . . .  10
         4.3     Second Product . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
         4.4     Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
         4.5     Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
                                                                                        
ARTICLE V FUTURE TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
                                                                                        
ARTICLE VI GRANT BACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
         6.1     Grant Back Rights  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
         6.2     Grant Back and Cancellation Term . . . . . . . . . . . . . . . . . . . . .  13
         6.3     Grant Back Royalties . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
         6.4     Grantback Milestone Payments . . . . . . . . . . . . . . . . . . . . . . .  14
         6.5     TBI Timely Payments  . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
         6.6     Accounting and Records . . . . . . . . . . . . . . . . . . . . . . . . . .  15
                                                                                        
ARTICLE VII ACCOUNTING AND RECORDS  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
         7.1     Accounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
         7.2     Payments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
         7.3     Records  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
         7.4     Conversions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
         7.5     Foreign Currency . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
         7.6     Income Taxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
                                                                                        
ARTICLE VIII TERM AND TERMINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
         8.1     Term of this Agreement . . . . . . . . . . . . . . . . . . . . . . . . . .  16
         8.2     Termination by TBI . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
</TABLE>





                                     -i-
<PAGE>   3
<TABLE>
<S>                                                                                            <C>
         8.3     Termination by ILEX  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
         8.4     Rights After Termination . . . . . . . . . . . . . . . . . . . . . . . . . .  16
                                                                                            
ARTICLE IX PROPRIETARY RIGHTS AND TECHNOLOGY ASSISTANCE . . . . . . . . . . . . . . . . . . .  17
         9.1     Right to Sue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
         9.2     No Duty to Enforce . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
         9.3     Diligent Prosecution of Existing Applications  . . . . . . . . . . . . . . .  17
         9.4     Furnishing of Technology . . . . . . . . . . . . . . . . . . . . . . . . . .  18
         9.5     Furnishing of Technical Assistance . . . . . . . . . . . . . . . . . . . . .  18
         9.6     Technology Meetings  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
         9.7     Confidentiality Terms  . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
                                                                                            
ARTICLE X FORCE MAJEURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
         10.1    Force Majeure  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  19
                                                                                            
ARTICLE XI NOTICES  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  19
         11.1    Notices  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  19
                                                                                            
ARTICLE XII WARRANTIES, REPRESENTATION AND INDEMNITY  . . . . . . . . . . . . . . . . . . . .  20
         12.1    Right to Grant and Complete Rights . . . . . . . . . . . . . . . . . . . . .  20
         12.2    Authorization  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  20
         12.3    Compliance with Appropriate Law  . . . . . . . . . . . . . . . . . . . . . .  20
         12.4    Responsibility for Compliance  . . . . . . . . . . . . . . . . . . . . . . .  20
         12.5    Limited Liability  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
         12.6    Warranty Indemnity . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
         12.7    ILEX General Indemnity . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
         12.8    TBI General Indemnity  . . . . . . . . . . . . . . . . . . . . . . . . . . .  22
         12.9    Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  22
         12.10   DISCLAIMER.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  22
         12.11   Insurance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  23
                                                                                            
ARTICLE XIII DISPUTE RESOLUTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  23
         13.1    Dispute Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  23
                                                                                            
ARTICLE XIV MISCELLANEOUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  24
         14.1    Severability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  24
         14.2    Entire Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  24
         14.3    Limitation of Authority  . . . . . . . . . . . . . . . . . . . . . . . . . .  24
         14.4    Choice of Law  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  24
         14.5    No Waiver  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  24
         14.6    Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  24
         14.7    Binding Agreement  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
         14.8    Counterparts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
         14.9    Headings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
         14.10   Prohibition of Use of Names  . . . . . . . . . . . . . . . . . . . . . . . .  25
         14.11   Patent Marking.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
</TABLE>





                                     -ii-
<PAGE>   4
<TABLE>
<S>                                                                                        <C>
   14.12   Responsibility for Expenses  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
   14.13   Amendments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
   14.14   Publicity  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
   14.15   Informed Review  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
                                                                                        
SCHEDULE 1.14 GRANT BACK TERRITORY  . . . . . . . . . . . . . . . . . . . . . . . . . . .  S-1.14-1
                                                                                        
SCHEDULE 1.32 PATENT RIGHTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  S-1.32-1
                                                                                        
SCHEDULE 1.44 TELIOS PATENT RIGHTS  . . . . . . . . . . . . . . . . . . . . . . . . . . .  S-1.44-1
                                                                                        
SCHEDULE 3.45 STOCK WARRANT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  S-3.45-1
</TABLE>





                                    -iii-
<PAGE>   5
                DRUG DEVELOPMENT AND COMMERCIALIZATION AGREEMENT

         This DRUG DEVELOPMENT AND COMMERCIALIZATION AGREEMENT (the
"AGREEMENT") is made this 27th of March, 1998 (the "EFFECTIVE DATE"), by and
between The Burnham Institute, a non-profit company organized and existing
under the laws of the State of California, and having its principal place of
business at 1091 North Torrey Pines Road, La Jolla, California 942037 ("TBI")
and ILEX Oncology, a company organized and existing under the laws of Delaware,
and having its principal place of business at 11550 IH 10 West, Suite 300, San
Antonio, Texas 78230 ("ILEX").

                                R E C I T A L S

         WHEREAS, TBI has developed and is the owner of certain Technology
further described below;

         WHEREAS, ILEX possesses drug development, manufacturing and
commercialization expertise related to development and marketing of
pharmaceuticals for the treatment of patients with cancer;

         WHEREAS, ILEX desires to obtain licenses under the Technology for the
purpose of further development and eventual commercial exploitation of Products
embodying the Technology; and

         WHEREAS, TBI is willing to grant such licenses to ILEX;

         NOW, THEREFORE, in consideration of the financial terms set forth
herein, as well as other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Parties hereto, intending to
be legally bound, hereby covenant, and agree as follows:


                                   ARTICLE I
                                  DEFINITIONS

         1.1     "AFFILIATES" shall mean any Person which, directly or
indirectly, owns, is owned by, or is under common ownership with a party to
this Agreement or any Person actually controlled by, controlling, or under
control of a party to this Agreement.  For the purposes of this definition,
"ownership" or "control" shall mean a Person owns or controls the lesser of (i)
fifty percent (50%)  and (ii) the maximum ownership interest permitted by law,
of the equity conferring votes, rights and/or otherwise has the ability to
direct the business affairs of another Person.

         1.2     "BASE CURRENCY" shall mean United States dollars.

         1.3     "COMMERCIAL SALE" shall mean the transfer of title to, lease
of or grant of right to use a Product to a Third Party who uses the Product in
the Field but specifically





                                     -1-
<PAGE>   6


excludes the transfer to an Affiliate or sublicensee who resells, markets or
distributes the Product.

         1.4     "COMPOUND" shall mean First Compound and Second Compound.

         1.5     "CREDITS" shall mean milestone payments actually made to TBI
which shall be fully creditable against any earned royalties which may be due
TBI under this Agreement.

         1.6     "DEFERRED MILESTONE" shall have the meaning as defined in
SECTION 4.4.

         1.7     "EFFECTIVE DATE" shall be the date set forth in the first
paragraph of this Agreement.

         1.8     "FDA" shall mean the U.S. Food and Drug Administration or any
successor entity.

         1.9     "FIELD" shall mean human therapeutic or prophylactic treatment
of cancer.

         1.10    "FIRST COMPOUND" shall mean THP conjugated to doxorubicin.

         1.11    "GAAP" shall mean generally acceptable accounting principles
for the United States.

         1.12    "GLP TOXICOLOGY" shall mean good laboratory practice
toxicology studies.

         1.13    "GRANT BANK RIGHTS" shall have the meaning as defined in
SECTION 6.1.

         1.14    "GRANT BACK TERRITORY" shall mean Japan and Asia, including
all of Russia, as further shown on the map attached hereto as SCHEDULE 1.14.

         1.15    "ILEX CLINICAL DATA" shall mean all clinical data and
information generated by or on behalf of ILEX and useful or required for filing
with a Regulatory Agency to market First Product or Second Product, as
applicable.

         1.16    "IDENTITY DATE" shall have the meaning given such term in
SECTION 4.3(i).

         1.17    "ILEX INDEMNITY CLAIM" shall have the meaning as defined in
SECTION 12.8(i).

         1.18    "INDEMNITY CLAIM" shall have the meaning as defined in SECTION
12.7(i).

         1.19    "IND" shall mean Investigational New Drug application as that
term is used by the FDA.



                                     -2-
<PAGE>   7
         1.20    "KNOW-HOW" shall include, without limitation, any now existing
technology, data, know-how, confidential information, compounds, processes,
formulae, materials, devices, systems, notes, records preparations, usage
information, procedures, regulatory information, manufacturing information,
proprietary and secret ideas, technical information, trade secrets, commercial
information, techniques, data or other information, whether in written or
verbal form, useful or related Patent Rights to THP, Compound or Products, or
the manufacturing of THP, Compound or Products.

         1.21    "MILESTONE 1" shall have the meaning as defined in SECTION
4.2(i).

         1.22    "MILESTONE 2" shall have the meaning as defined in SECTION
4.2(ii).

         1.23    "MILESTONE 3" shall have the meaning as defined in SECTION
4.2(iii).

         1.24    "MILESTONE 4" shall have the meaning as defined in SECTION
4.2(iv).

         1.25    "MILESTONE 5" shall have the meaning as defined in SECTION
4.2(v).

         1.26    "MILESTONE 6" shall have the meaning as defined in SECTION
4.2(vi).

         1.27    "MILESTONE 7" shall have the meaning as defined in SECTION
4.2(vii).

         1.28    "MILESTONE 8" shall have the meaning as defined in SECTION
4.2(viii).

         1.29    "NDA" shall mean New Drug Application as that term is used in
the FDA.

         1.30    "NET SALES" shall mean the amount of money or other
consideration received by ILEX, its Affiliates or sublicensees for Commercial
Sales of Products after deducting:

                 (i)      the normal or customary trade and/or quantity
                          discounts and allowances actually given to customers
                          for the particular Commercial Sale;

                 (ii)     refunds, rebates and allowances for returned, damaged
                          goods or outdated Product;

                 (iii)    excise and sales taxes, customs duties, tariffs and
                          other governmental charges actually included in the
                          Net Sales;

                 (iv)     separately identifying costs of transportation
                          (including without limitation transportation packing
                          and transportation insurance) if actually paid by the
                          Customer and actually included in the Net Sales;





                                     -3-
<PAGE>   8
                 (v)      retroactive price reductions applicable to Net Sales
                          that are actually allowed or granted.

Notwithstanding the foregoing, if a Product is sold in conjunction with or
includes Royalty Bearing Components, Net Sales for purposes of determining
royalties payable under this Agreement shall be calculated as the product
obtained by using whichever of the following formulas is applicable:

                 (a)      if both the Compound and the Royalty Bearing
                          Components included in the combination products or
                          service are also sold separately (by ILEX or others),
                          multiplying Net Sales of the combination products or
                          service by the fraction A/(A+B), where "A" is the
                          price during the royalty paying period in question of
                          the Compound if sold separately and "B" is the price
                          of the Royalty Bearing Components in the combination
                          products or service if sold separately.

                 (b)      if SECTION 1.30(a) does not apply, multiplying Net
                          Sales of such combination products or service by the
                          fraction C/(C+D) in which "C" is the Valuation of the
                          Compound portion of such combination products or
                          service and "D" is the Valuation of the Royalty
                          Bearing Components in the combination products or
                          service; provided, however, if the Parties cannot
                          agree on the Valuation of the components of the
                          Product then each Party agrees to binding
                          determination of Valuation by a single independent
                          arbitrator with experience in valuation of similar
                          products.  Within thirty (30) days of either Party
                          requesting such determination, the arbitrator will be
                          designated in accordance with ARTICLE XIII.  After
                          such arbitrator is designated, each Party shall have
                          twenty (20) days to submit its Valuation and written
                          support for its Valuation.  The arbitrator shall have
                          an additional twenty (20) business days to designate
                          one of the Party's Valuations as the Valuation for
                          the Parties to use.

         1.31    "PARTY" or "PARTIES" shall mean TBI and/or ILEX as
appropriate.

         1.32    "PATENT RIGHTS" shall mean any and all existing patents and
patent applications licensed to or owned by TBI which relate to THP, Compound
or Products, as listed on SCHEDULE 1.32, as amended from time to time, and any
and all patents and patent applications which claim priority from any such
patent or application including without limitation all divisional, reissue,
re-examination, continuation, and continuations-in-part (but only to the extent
such continuations-in-part claims subject matter embraced by a patent or patent
applications now existing), extensions and renewal applications and





                                     -4-
<PAGE>   9

patents thereof and any and all other counterpart applications in any countries
and patents and inventors' certificates, utility models and the like issuing
therefrom.

         1.33    "PERSON" shall mean and include any individual, corporation,
partnership, joint venture, trust, unincorporated organization, university,
college or government or any agency or political subdivision thereof.

         1.34    "PHASE I" shall mean Phase I clinical trials as defined by the
FDA.

         1.35    "PHASE II" shall mean Phase II clinical trials as defined by
the FDA.

         1.36    "PHASE III" shall mean Phase III clinical trials as defined by
the FDA.

         1.37    "PRODUCT" shall mean a therapeutic agent which is comprised,
at least in part, of the First Compound or the Second Compound, as applicable,
and may include Royalty Bearing Components and non-Royalty Bearing components.
Nothing in this definition shall be construed to grant any license rights
broader than the license rights granted in SECTIONS 2.1 AND 2.2.

         1.38    "REGULATORY AGENCY" shall mean the FDA and any corresponding
agencies in other countries where Product is to be sold or used.

         1.39    "ROYALTY BEARING COMPONENTS" shall mean all (i) components,
devices or products which are sold or are included as a part of a Product
and/or (ii) methods or processes which are used in conjunction with a Product
and for which either (i) ILEX must license and pay a royalty to a Third Party
or (ii) ILEX owns a patent covering the component, device, product, method, or
process in the appropriate country where such component, product or device is
sold or method or process is used.

         1.40    "SECOND COMPOUND" shall mean THP conjugated to an (i)
anthracycline or (ii) other cytotoxic agent that ILEX has the exclusive right
to develop for use in the Field in a country.

         1.41    "SUBSEQUENT CALENDAR YEAR" shall have the meaning as defined
in SECTION 3.3.

         1.42    "TECHNOLOGY" shall mean any and all now existing proprietary
rights of TBI related to THP, Compound, Products, the manufacturing of THP,
Compounds or Products or Patent Rights, including Patent Rights and Know-How,
throughout the territory, whether or not protectable by patent, trade secret,
copyright, or other intellectual property laws.

         1.43    "TELIOS KNOW-HOW" shall include, without limitation, any now
existing technology, data, know-how, confidential information, compounds,
processes, formulae, devices, systems, notes, records preparations, usage
information, materials, procedures,





                                     -5-
<PAGE>   10

regulatory information, manufacturing information, proprietary and secret
ideas, technical information, trade secrets, commercial information,
techniques, data or other information, whether in written or verbal form,
useful or related to the Telios Patent Rights.

         1.44    "TELIOS PATENT RIGHTS" shall mean any and all patent and
patent applications licensed to or owned by TBI as listed on SCHEDULE 1.44, as
amended from time to time, and any and all patents and patent applications
which claim priority from any such patent or application including without
limitation all divisional, reissue, re-examination, continuation, and
continuations-in-part (but only to the extent such continuation-in-part claims
subject matter embraced by a patent or patent application now existing),
extensions and renewal applications and patents thereof and any and all other
counterpart applications in any countries and patents and inventors'
certificates, utility models and the like issuing therefrom.

         1.45    "TELIOS TECHNOLOGY" shall mean any and all now existing
proprietary rights of TBI related to the Telios Patent Rights, including Telios
Patent Rights and Telios Know-How, throughout the territory, whether or not
protectable by patent, trade secret, copyright, or other intellectual property
laws.

         1.46    "TERRITORY" shall mean all the countries of the world and
their respective territories and possessions, unless and until TBI exercises
the Grant Back Rights as provided in SECTION 6.2 and thereby removes the Grant
Back Territory from the Territory.

         1.47    "THIRD PARTY" shall mean any party other than TBI, ILEX and
their respective Affiliates.

         1.48    "THP" shall mean tumor homing peptides, including, without
limitation, peptides, polypeptides, proteins and fragments of a protein, which
home to a selected organ, tissue or cell, all as claimed in the Patent Rights.

         1.49    "THP-DRUG" shall mean THP conjugated to a chemotherapeutic
and/or chemopreventive agent which, within sixty (60) months of the Effective
Date is acquired, developed or conceived by or for TBI, and is disclosed to TBI
within six (6) months after the end of such sixty (60) months period, and TBI
is entitled to license to others.

         1.50    "VALUATION" for any Compound or Royalty Bearing Component in a
Product shall mean the determination of the relative contribution of the
Compound or Royalty Bearing Component to the overall value of the Product.


                                     -6-
<PAGE>   11

(Confidential treatment has been requested for portions of this page.  The
confidential portions have been redacted and are denoted by [**].  The
confidential portions have been separately filed with the Securities and
Exchange Commission.)


                                   ARTICLE II
                                    LICENSE

         2.1     LICENSE TO TECHNOLOGY.  Subject to the terms and conditions of
this Agreement, effective as of the Effective Date, TBI grants to ILEX an
exclusive license under the Technology in the Territory in the Field to make,
have made, use, rent, sell, lease, import, sublicense, market, improve and
otherwise commercially exploit the First Compound or Second Compound, as
applicable; provided, this license shall not include Second Compound unless
ILEX exercises its option under SECTION 4.3; provided further, if ILEX
exercises its option under SECTION 4.3, this license shall not include First
Compound.

         2.2     LICENSE TO TELIOS TECHNOLOGY.  Subject to the terms and
conditions of this Agreement, effective as of the Effective Date, TBI grants to
ILEX a nonexclusive license under the Telios Technology in the Territory in the
Field to make, have made, use, rent, sell, lease, import, sublicense, market,
improve and otherwise commercially exploit the First Compound or Second
Compound, as applicable; provided, however, ILEX shall only use the Telios
Technology in connection with the exercise of its rights granted by TBI under
SECTION 2.1.


                                  ARTICLE III
                                 CONSIDERATION

         3.1     EARNED ROYALTIES.  ILEX shall pay TBI a royalty based upon
annual Net Sales calculated on a calendar year basis as set forth below:


<TABLE>
  <S>                                                        <C>
               ANNUAL NET SALES                              ANNUAL ROYALTY RATE
               ----------------                              -------------------
               up to $50,000,000                                    [**]
  greater than $50,000,000 up to $150,000,000                       [**]
  greater than $150,000,000 up to $250,000,000                      [**]
  greater than $250,000,000 up to $500,000,000                      [**]
  greater than $500,000,000                                         [**]
</TABLE>

         The annual royalty rate shall not retroactively apply.  For means of
illustration, but not limitation, if annual Net Sales totaled $300,000,000 in
any given year, earned royalties would equal $50,000,000 x [**] + $100,000,000
x [**] + $100,000,000 x [**] + $50,000,000 x [**].

                                     -7-
<PAGE>   12

(Confidential treatment has been requested for portions of this page.  The
confidential portions have been redacted and are denoted by [**].  The
confidential portions have been separately filed with the Securities and
Exchange Commission.)


         3.2     ACCRUED ROYALTIES.  Notwithstanding SECTION 1.3, no royalty
shall be payable on Product made, sold or used for tests or developmental
purposes or distributed as samples or in connection with clinical studies.  No
multiple royalty shall be payable because the manufacture, use or sale of
Product is covered by more than one patent within the Patent Rights.

         3.3     MINIMUM ROYALTIES.  In the first full calendar year after
approval of an NDA ("Subsequent Calendar Year") and each year thereafter, the
royalties payable by ILEX under SECTION 3.1 shall not be less than the
following:


<TABLE>
<CAPTION>
                    CALENDAR YEAR                            MINIMUM ROYALTIES PAYABLE
                    -------------                            -------------------------
  <S>                                                                <C>
  First Subsequent Calendar Year                                        [**]

  Second Subsequent Calendar Year                                       [**]

  Third Subsequent Calendar Year                                        [**]

  Fourth Subsequent Calendar Year                                       [**]

  Fifth Subsequent Calendar Year                                        [**]

  Sixth Subsequent Calendar Year and All Subsequent                     [**]
  Calendar Years Thereafter
</TABLE>

         In the event that the annual earned royalties either paid by ILEX or
reduced by Credits in any Subsequent Calendar Year are less than the minimum
royalties due for such year, then:

         (i)     either Party, at it discretion, may elect to terminate this
                 Agreement;

         (ii)    ILEX and TBI can mutually agree to convert the exclusive
                 license granted herein to a non-exclusive license; provided,
                 in the event that the Parties agree to convert the exclusive
                 license granted herein to a non-exclusive license, the
                 royalties described in SECTION 3.1 shall decrease by fifty
                 percent (50%) and the minimum royalties described in this
                 SECTION 3.3 shall no longer be applicable.

         3.4     PAYMENT OF MINIMUM ROYALTIES.  ILEX shall pay TBI one quarter
(1/4) of the applicable yearly minimum royalties within sixty (60) days of the
close of each calendar quarter.  Notwithstanding the foregoing if this
Agreement is terminated or expires prior to the end of any calendar year, the
minimum royalties provided for in this SECTION 3.3 shall be decreased on a pro
rata basis.


                                     -8-
<PAGE>   13


(Confidential treatment has been requested for portions of this page.  The
confidential portions have been redacted and are denoted by [**].  The
confidential portions have been separately filed with the Securities and
Exchange Commission.)


         3.5     STOCK WARRANT.  ILEX hereby grants TBI warrants to purchase
ILEX common stock as set forth in SCHEDULE 3.5.

         3.6     MILESTONE PAYMENTS.  Subject to fulfillment of preconditions
to payment referred to in this SECTION 3.6, ILEX shall pay TBI the following
sums which shall be deemed to be Credits:

                 (i)      [**] within thirty (30) days after the first
                          completion of Milestone 1;

                 (ii)     [**] within thirty (30) days after the first
                          completion of Milestone 2;

                 (iii)    [**] within thirty (30) days after the first
                          completion of Milestone 3; and

                 (iv)     [**] within thirty (30) days after the first
                          completion of Milestone 8.


         ILEX shall be obligated to pay the aforementioned milestone payments,
only a single time, whether or not ILEX abandons development of First Product,
which payment shall be deemed to be Credits.

         3.7     LICENSE FEE.  ILEX shall pay TBI Two hundred fifty thousand
dollars ($250,000) upon execution of this Agreement (which shall not constitute
Credits).

         3.8     REDUCTION OF ROYALTIES.     Notwithstanding anything to the
contrary in this Article III:

                 (a)      For five (5) years after the date of the first
                          Commercial Sale of a Product in any country, ILEX,
                          will pay royalties at the rate specified in SECTION
                          3.1 on all Commercial Sales of Products in said
                          country.

                 (b)      Payment of royalties on Net Sales made in any country
                          shall continue after the end of the five (5) year
                          period specified in (a) above if by that time TBI
                          shall have received a notice of allowance, in any of
                          the applications included in the Patent Rights, of a
                          claim or claims that would be infringed by the
                          Commercial Sale of Product by ILEX, its affiliates or
                          its sublicensees in any country ("Applicable Claim")
                          in the Territory but for the licenses granted herein.

                 (c)      If, at the end of the five (5) year period specified
                          in (a) above, no Applicable Claim has been allowed in
                          any country, the royalties




                                     -9-
<PAGE>   14

(Confidential treatment has been requested for portions of this page.  The
confidential portions have been redacted and are denoted by [**].  The
confidential portions have been separately filed with the Securities and
Exchange Commission.)


                          payable on Net Sales made in any country shall be
                          reduced to sixty percent (60%) of the royalty rate
                          specified in SECTION 3.1 until an Applicable Claim is
                          allowed in any country or until the end of ten (10)
                          years from the date of the first Commercial Sale of a
                          Product in any country, whichever occurs first.  Upon
                          allowance of an Applicable Claim in that country,
                          payment of royalties at the rate specified in SECTION
                          3.1 shall be resumed and will continue thereafter for
                          the term of this Agreement.  If no Applicable Claim
                          is allowed in any country after ten (10) years from
                          the first Commercial Sale of a Product in any
                          country, no further royalties will be owed on Net
                          Sales made in any country.


                                   ARTICLE IV
                     CLINICAL DEVELOPMENT AND MANUFACTURING

         4.1     CLINICAL DEVELOPMENT.  ILEX shall use its best efforts to
commercially develop and market Products.

         4.2     DEVELOPMENT PLAN MILESTONES.  ILEX'S best efforts obligations
set forth in SECTION 4.1 shall be deemed fulfilled if ILEX completes the
following milestones in the times prescribed or any extensions as provided in
this ARTICLE IV or by mutual agreement.

                 (i)      ILEX shall have [**] months from the Effective Date
                          to synthesize First Product and confirm TBI's in vivo
                          studies ("MILESTONE 1").

                 (ii)     ILEX shall have [**] months from the Effective Date
                          to initiate GLP Toxicology studies ("MILESTONE 2").

                 (iii)    ILEX shall have [**] months from the Effective Date
                          to file the IND ("MILESTONE 3").

                 (iv)     ILEX shall have [**] months from the Effective Date
                          to complete Phase I trials ("MILESTONE 4").

                 (v)      ILEX shall have [**] months from the Effective Date
                          to complete Phase II trials ("MILESTONE 5").

                 (vi)     ILEX shall have [**] months from the Effective Date
                          to complete Phase III trials ("MILESTONE 6").

                 (vii)    ILEX shall have [**] months from the Effective Date
                          to file the NDA in the United States ("MILESTONE 7").





                                     -10-
<PAGE>   15

(Confidential treatment has been requested for portions of this page.  The
confidential portions have been redacted and are denoted by [**].  The
confidential portions have been separately filed with the Securities and
Exchange Commission.)


                 (viii)   After completion of Milestone 7, ILEX shall
                          diligently pursue FDA approval of an NDA.  Upon
                          receipt of FDA approval of an NDA ("MILESTONE 8"),
                          ILEX's development efforts shall be deemed fulfilled.

         4.3     SECOND PRODUCT.  ILEX, at its discretion, may abandon the
development of First Product at any time after Milestone 3 and before
completion of Milestone 5, including any extensions thereof, by providing TBI
written notice of ILEX's intention to abandon further development of First
Product prior to completion of Milestone 5.  If ILEX abandons the development
of First Product, ILEX may develop Second Product; provided:

                 (i)      ILEX provides TBI written notice of the identity of
                          Second Product within sixty (60) days after providing
                          TBI notice of its intention to abandon ("Identity
                          Date"); and

                 (ii)     The development timetable for Second Product,
                          including the right to purchase milestone extensions,
                          will be the same as for First Product, except that
                          milestone dates will be measured from the Identity
                          Date.

         If ILEX elects to abandon the development of First Product and does
not elect to develop Second Product, this Agreement shall terminate.  If ILEX
elects to abandon the development of First Product, then all rights to First
Product shall revert to TBI, and all related Know-How and ILEX Clinical Data
shall be made available to TBI for potential use with First Product, and TBI
shall be entitled to pursue whatever commercialization of First Product as TBI
deems appropriate.

         4.4     EXTENSIONS.  ILEX, at its discretion, may defer for one (1)
year any one of Milestone 4, Milestone 5, Milestone 6, Milestone 7 or Milestone
8 ("DEFERRED MILESTONE") of SECTION 4.2 and/or SECTION 4.3 by paying a
milestone extension fee as follows:

                 (i)      [**], if said milestone extension fee is paid prior
                          to Milestone 4;

                 (ii)     [**], if said milestone extension fee is paid prior
                          to Milestone 5.

                 (iii)    [**], if said milestone extension fee is paid prior
                          to Milestone 6.

                 (iv)     [**], if said milestone extension fee is paid prior
                          to Milestone 7.



                                     -11-
<PAGE>   16

Once such milestone extension fee is paid, the times specified in SECTIONS 4.2
OR 4.3 for all subsequent milestones shall be deferred for one (1 year).  The
milestone extension fee shall not be deemed to be Credits.

         4.5     TERMINATIONS.  In the event that (i) ILEX fails to meet any
milestone of SECTION 4.2 and (ii) ILEX fails to meet any Deferred Milestone of
SECTION 4.4, as applicable, TBI may, upon prior written notice, terminate this
Agreement.  In the event that ILEX objects to such termination, ILEX and TBI
will submit the question of whether ILEX has used its best efforts to develop
First Product or Second Product, as applicable, to binding arbitration as
provided for in ARTICLE XIII.  If the arbitrator determines that ILEX has used
its best efforts to develop First Product or Second Product, as applicable, the
arbitrator shall set a revised timetable for any remaining milestones and
determine what, if any, additional milestone extension fee should be reasonably
paid by ILEX.  Any such additional milestone extension fee shall not be deemed
to be Credits.  If the arbitrator determines that ILEX has failed to use its
best efforts to develop First Product or Second Product, as applicable to the
Dispute, TBI, at its discretion, may terminate this Agreement.

                                   ARTICLE V
                               FUTURE TECHNOLOGY

         Conditional upon ILEX fully complying with all of ILEX's material
obligations under this Agreement, ILEX shall have a right of first negotiation
to license each THP-Drug developed by or for TBI.  TBI shall in good faith
negotiate such license agreements with ILEX during the period of sixty (60)
days following TBI's request to ILEX as to whether ILEX desires to license a
particular THP-Drug and delivery by TBI to ILEX of a detailed written
description of such THP- Drug and applicable proprietary rights.  If the
Parties fail to enter such a license agreement on mutually agreeable terms for
any THP-Drug, TBI may undertake the commercial exploitation of such THP-Drug
itself or license such THP-Drug to a Third Party; provided, however, (i) as to
any THP-Drug for which ILEX has so expressed a desire to license, and subject
to the condition set forth in the first sentence hereof,TBI shall not enter a
license agreement related to such THP-Drug with a Third Party on more favorable
terms to the Third Party than TBI offered to ILEX for a period of five (5)
years after the date of such offer and (ii) the Parties' failure to enter a
license agreement for any one THP-Drug shall not affect ILEX's right of first
negotiation in any other THP-Drug.  TBI shall provide ILEX information related
to each THP-Drug in a timely manner after such THP Drug information is
developed by or for and received by TBI during the first five (5) years after
the Effective Date.



                                     -12-
<PAGE>   17

(Confidential treatment has been requested for portions of this page.  The
confidential portions have been redacted and are denoted by [**].  The
confidential portions have been separately filed with the Securities and
Exchange Commission.)


                                   ARTICLE VI
                                   GRANT BACK

         6.1     GRANT BACK RIGHTS.  Upon TBI's written request in accordance
with SECTION 6.2:

                 (i)      ILEX shall release back to TBI all rights granted by
                          TBI to ILEX under this Agreement in the Grant Back
                          Territory;

                 (ii)     ILEX shall grant TBI (with the right to grant
                          sublicenses to a Third Party who will commercially
                          exploit Products in the Field) an exclusive right to
                          use the ILEX Clinical Data in connection with seeking
                          approval of First Product or Second Product, as
                          applicable, from the appropriate Regulatory Agency in
                          the Grant Back Territory.

                 (iii)    ILEX shall deliver copies of the ILEX Clinical Data
                          to TBI in a timely manner after ILEX Clinical Data is
                          developed and received by ILEX.

(collectively the "GRANT BACK RIGHTS").

         Notwithstanding the foregoing, TBI shall have the option to cancel the
Grant Back Rights ("Cancellation Right") as provided in Section 6.2.  Upon
TBI's exercise of its Cancellation Right, the rights of ILEX under this
Agreement shall extend worldwide to include the Grant Back Territory and the
defined term Territory shall mean worldwide.

         6.2     GRANT BACK AND CANCELLATION TERM.  TBI, at its discretion may
elect to exercise its Grant Back Rights at any time prior to the first
anniversary of the Effective Date by providing ILEX written notice of said
election.  The Grant Back Rights shall automatically terminate if not exercised
prior to the first anniversary of the Effective Date.  TBI, at its discretion
may elect to exercise its Cancellation Right at any time prior to thirty (30)
days after ILEX provides TBI written notice of FDA acceptance of the IND and
ILEX's commencement (i.e., enrollment of first patient) of Phase I.  The
Cancellation Right shall automatically terminate if not exercised prior to
thirty (30) days after ILEX provides written notice of FDA acceptance of the
IND and ILEX's commencement (i.e., enrollment of first patient) of Phase I.

         6.3     GRANT BACK ROYALTIES. If TBI exercises its Grant Back Rights,
TBI shall pay ILEX [**] of the royalties received by TBI on Net Sales in the
Grant Back Territory; provided, TBI shall not be obligated to pay to ILEX for
any calendar year Grant Back royalties greater than [**] of the earned
royalties calculated and paid by ILEX to TBI for such calendar year under
SECTION 3.1.  If TBI enters into a transaction pursuant to which TBI receives
less than a commercially reasonable and customary earned royalty rate on Net
Sales in the Grant Back Territory and TBI receives other consideration in such
transaction, no matter how characterized, then TBI shall


                                     -13-
<PAGE>   18

(Confidential treatment has been requested for portions of this page.  The
confidential portions have been redacted and are denoted by [**].  The
confidential portions have been separately filed with the Securities and
Exchange Commission.)


nevertheless pay to ILEX [**] of a commercially reasonable and customary earned
royalty rate on said Net Sales in the Grant Back Territory.  If the Parties
cannot agree on the commercially reasonable and customary earned royalty, then
each Party agrees to binding determination of a commercially reasonable and
customary earned royalty by a single independent arbitrator with experience in
valuation of similar products.  Within thirty (30) days of either Party
requesting such determination, the arbitrator will be designated in accordance
with ARTICLE XIII.  After such arbitrator is designated, each Party shall have
twenty (20) days to submit its commercially reasonable and customary earned
royalty and written support for its commercially reasonable and customary
earned royalty.  The arbitrator shall have any additional twenty (20) business
days to designate one of the Party's commercially reasonable and customary
earned royalty as the commercially reasonable and customary earned royalty for
the Parties to use.

         6.4     GRANTBACK MILESTONE PAYMENTS.  If (i) TBI exercises its Grant
Back Rights and (ii) the preconditions described in this SECTION 6.4 are
fulfilled, TBI shall pay ILEX the following milestone payments.

                 (i)      [**] within thirty (30) days after ILEX provides
                          written notice of FDA acceptance of the IND and
                          ILEX's commencement (i.e., enrollment of first
                          patient) of Phase I;

                 (ii)     [**] within thirty (30) days after ILEX provides
                          written notice of FDA approval to commence and ILEX's
                          commencement (i.e., enrollment of first patient) of
                          Phase II; and

                 (iii)    [**] within thirty (30) days after ILEX provides
                          written notice of FDA approval to commence and ILEX's
                          commencement (i.e., enrollment of first patient) of
                          Phase III trials.

         Notwithstanding the foregoing, if TBI exercises its Cancellation Right
before ILEX provides written notice of FDA acceptance of the IND and ILEX's
commencement (i.e., enrollment of first patient) of Phase I, TBI shall not be
required to pay the applicable milestone payments described above.  If TBI
exercises its Cancellation Right after ILEX provides written notice of FDA
acceptance of the IND and ILEX's commencement (i.e., enrollment of first
patient) of Phase I, but before thirty (30) days after ILEX provides such
written notice, the [**] milestone payment of Section 6.4(i) shall be deemed a
Credit in such amount and TBI shall not be required to pay the applicable
milestone payments described above.

         6.5     TBI TIMELY PAYMENTS.  If TBI fails to timely make any payments
due under this ARTICLE VI, then ILEX shall be entitled to credit any such
deficiency against any payment ILEX owes TBI including milestone and minimum
royalty payments.





                                     -14-
<PAGE>   19

         6.6     ACCOUNTING AND RECORDS.  In the event TBI exercises its Grant
Back Rights, like obligations to those of ARTICLE VII shall be deemed agreed to
by TBI.


                                  ARTICLE VII
                             ACCOUNTING AND RECORDS

         7.1     ACCOUNTING.  During the term of this Agreement, ILEX shall
furnish to TBI a written report within sixty (60) days after the close of each
calendar quarter (March 31, June 30, September 31 and December 31) ("ROYALTY
PERIOD") showing (i) Net Sales during the Royalty Period, (ii) the earned
royalties in the Base Currency, (iii) withholding taxes, if any, required by
law to be deducted, (iv) the official exchange rates used in determining the
earned royalties and (v) the earned royalties payable and/or deducted from any
Credits.

         7.2     PAYMENTS.  All payments required under this Agreement shall be
paid in the Base Currency to the address applicable under SECTION 11.1 of this
Agreement or to such other place as the Party receiving payment may reasonably
designate consistent with applicable laws and regulations.  All earned royalty
payments shall be due and payable by the date the applicable royalty report is
due.

         7.3     RECORDS.  For a period of three (3) years after the date
covered by any report provided under SECTION 7.1, ILEX agrees to maintain
written records with respect to its operations for such period pursuant to this
Agreement in sufficient detail to enable TBI or its designated accountants to
compute the amount of royalties or payments payable to TBI, and further agrees
to permit said records to be audited from time to time, on reasonable notice
during normal business hours to the extent necessary to verify the amount of
royalties or payments due hereunder; provided TBI shall not be entitled to
perform more than one (1) audit in any calendar year.  Any such audit shall be
conducted by an independent auditor selected by TBI and approved by ILEX.  Any
such auditor shall execute a confidentiality agreement satisfactory to ILEX.
Any report by such auditor shall only state that the amounts of royalties or
payments were accurate or state the specific amount overpaid or underpaid.  A
copy of such report shall be provided to both ILEX and TBI.  TBI shall pay the
costs of said examination unless an underpayment of greater than ten percent
(10%) in royalties due is present, in which case ILEX shall reimburse TBI for
the reasonable expenses of the examination.

         7.4     CONVERSIONS.  Earned royalty payments on any sales in any
country outside the United States shall be calculated in the Base Currency in
accordance with ILEX's standard accounting procedures used for ILEX's reporting
of income to its stockholders and for other external reporting, which shall
comply with GAAP.

         7.5     FOREIGN CURRENCY.  Each Party shall use its best efforts to
convert the payments due the other Party on sales in any country to the Base
Currency; provided,





                                     -15-
<PAGE>   20

however, that if conversion to and transfer of the Base Currency cannot be made
in any country for any reason, at the election of the Party receiving such
royalties, any such payment (i) may be made in the currency of the country in
which such sales are made and deposited in the receiving Party's name in a bank
designated by the receiving Party in any such country; or (ii) the obligation
of a Party to pay such earned royalties shall be suspended and accrued until
such conversion and transfer of all funds by such Party becomes possible.

         7.6     INCOME TAXES.  If a governmental entity requires that ILEX
withhold and pay income taxes assessed or imposed against or required to be
withheld and paid to such entity from payments due TBI, then such withheld and
paid sums shall be deducted from amounts payable hereunder and shall be paid to
appropriate fiscal or tax authorities on behalf of TBI.  Tax receipts received
by ILEX evidencing payment of such taxes shall be forwarded to TBI.


                                  ARTICLE VIII
                              TERM AND TERMINATION

         8.1     TERM OF THIS AGREEMENT.  Unless sooner terminated as otherwise
provided herein, this Agreement shall terminate on the expiration of the last
of any issued patents in the Patent Rights and/or Telios Patent Rights to
expire, and thereafter ILEX shall have a fully paid-up license to make, have
made, use, rent, sell, lease, market, sublicense and otherwise commercially
exploit the Technology and Telios Technology for the Product in the Field in
the Territory.

         8.2     TERMINATION BY TBI.  TBI may terminate this Agreement if ILEX
fails to perform any of its material obligations under this Agreement and fails
to remedy said breach within ninety (90) days after being given written notice
of the specific failure or default and termination by TBI; provided, if the
default is for non-payment of money, then the remedy period shall be thirty
(30) days rather than ninety (90) days.

         8.3     TERMINATION BY ILEX.  ILEX may terminate this Agreement on
thirty (30) days written notice to TBI for any reason.

         8.4     RIGHTS AFTER TERMINATION.  In the event this Agreement is
terminated under SECTION 8.2 OR SECTION 8.3:

                 (i)      ILEX shall have one hundred twenty (120) days to
                          complete the manufacture and two hundred forty (240)
                          days to complete sale or license of any Products in
                          stock or in the course of manufacture at the time of
                          termination, all subject, however, to payments of
                          royalty and accounting as provided





                                     -16-
<PAGE>   21


                          herein, even if such royalty obligations arise from
                          transactions subsequent to the effective date of
                          termination;

                 (ii)     ILEX's obligation to pay royalties and its obligation
                          to keep records and to allow a final audit will
                          survive any termination; and

                 (iii)    Except as expressly provided herein, no Party
                          hereunder shall be discharged or relieved from any
                          liability or obligation existing prior to such
                          termination.

                                   ARTICLE IX
                  PROPRIETARY RIGHTS AND TECHNOLOGY ASSISTANCE

         9.1     RIGHT TO SUE.  Each Party shall promptly inform the other of
any suspected infringement of any Patent Rights or misuse, misappropriation,
theft or breach of confidence of other proprietary rights in the Technology by
a Third Party.  With respect to such activities as are suspected and if such
activities are a violation of ILEX's rights, ILEX shall have the right, but not
the obligation, to bring suit against a Third Party for infringement, misuse,
misappropriation, theft or breach of confidence of the proprietary rights
against such Third Party.  ILEX, if required by law, may join TBI as a Party to
the suit at ILEX's expense.  In the event that ILEX prosecutes any such
lawsuit, then ILEX shall be entitled to deduct its costs and expenses from any
damages it is awarded.  Any remaining damage awarded shall be divided
seventy-five percent (75%) to ILEX and twenty-five percent (25%) to TBI.
Before any action is taken that will affect the validity of any rights
(including the Patent Rights) or before such lawsuit is settled or compromised,
the Parties shall consult and cooperate with one another to insure that the
rights granted by this Agreement (including the Patent Rights) are not
materially affected by any such acts, settlement or compromise.  TBI shall
cooperate fully in any such lawsuit and shall not take or omit any significant
action which would interfere with ILEX's prosecution of such a lawsuit.

         9.2     NO DUTY TO ENFORCE.  ILEX shall be entitled to determine and
carry out, in its discretion, the course of action, if any, that it may deem
appropriate for responding to instances of Third Party infringement of any
Patent Rights licensed hereunder or misuse, misappropriation, or breach of
confidence or other proprietary rights in the Technology licensed hereunder.
In such regard, ILEX shall have no obligation to TBI regarding ILEX's decision
whether to take action or regarding any course of action ILEX may choose to
take.

         9.3     DILIGENT PROSECUTION OF EXISTING APPLICATIONS.  TBI shall
diligently prosecute and maintain all patents and patent applications within
the Patent Rights; provided, however, ILEX shall reimburse TBI for all
reasonable past and future expenses incurred by TBI for such prosecution and
maintenance, which reimbursement shall be made within



                                     -17-
<PAGE>   22

sixty (60) days after the invoice  therefor is received by ILEX.  In the event
TBI elects to abandon or not to maintain any patent or patent application
related to the Technology or not to file any counterpart application in any
country, TBI shall promptly provide ILEX written notice, which notice shall in
no event be provided later than thirty (30) days prior to any filing or
response deadline.  ILEX, at its discretion, may prosecute and maintain any
such patent or patent application.  TBI shall cooperate and causes its
employees and agents to cooperate with ILEX in any such prosecution or
maintenance.  If at any time TBI transfers any rights under any of the Patent
Rights to a Third Party then ILEX's obligations to reimburse TBI for all
reasonable future expenses incurred by TBI thereafter for such prosecution and
maintenance shall be decreased on a pro-rata basis for each such license.

         9.4     FURNISHING OF TECHNOLOGY.  TBI shall provide ILEX with all the
information and documents in its possession, and which are reasonably necessary
to practice the Technology.

         9.5     FURNISHING OF TECHNICAL ASSISTANCE.  Upon reasonable advance
notice, TBI shall provide to ILEX, at the sole expense of ILEX, skilled
personnel to assist ILEX in implementing the Technology.

         9.6     TECHNOLOGY MEETINGS.  The Parties shall meet bi-yearly
(January and July) to discuss the research being conducted by TBI on the
therapeutic applications of THP-Drug conjugates and their use.  All these
conversations shall be subject to the confidentiality provisions of SECTION
9.7.

         9.7     CONFIDENTIALITY TERMS.  The Parties agree to maintain the
confidentiality of all the confidential information disclosed in any meetings
under SECTION 9.6 or otherwise disclosed by one Party to the other Party.  The
Parties will afford the same level of protection that they use for their own
confidential information, but in any event at least commercially reasonable
level of protection, to protect the other Party's confidential information.
The term confidential information shall not include material which was in the
public domain or becomes public domain other than through a breach of this
confidentiality undertaking on the part of the receiving Party or as received
by the receiving Party from a Third Party that is not under a confidential
obligation to the disclosing Party or is known to the receiving Party as shown
by written record prior to disclosure at the meeting or as developed by the
receiving Party without access to the confidential information which has been
disclosed or is generally made available to the public by the disclosing Party
without restrictions on disclosure.


                                     -18-
<PAGE>   23
                                   ARTICLE X
                                 FORCE MAJEURE

         10.1    FORCE MAJEURE.   Except as otherwise provided in this
Agreement, any delay or failure to perform under this Agreement arising from a
force majeure event as specified herein shall not be deemed to be a default and
shall not put an end to this Agreement, so that the same shall continue in
suspense or part performance until such event shall have ceased.  For the
purpose of this Article, a force majeure event is a labor strike, labor
lockout, civil commotion, riot, invasion, war, fire, explosion, storm, flood,
earthquake or governmental order.  Further, any such force majeure event shall
be applicable only (i) if said event causes more than a thirty (30) day delay
in the Party's ability to perform under this Agreement; and (ii) if the Party
affected by such event shall notify the other Party within three (3) days after
the initial occurrence thereof, and again within three (3) days after the
running of the thirty (30) day delay; and (iii), if such Party uses its best
efforts based on reasonable business judgment to eliminate the cause of such
event as soon as is reasonably feasible.  Notwithstanding the foregoing, this
Section 10.1 shall not under any circumstances permit, cause or result in a
delay of the five (5) year first negotiation period specified in Article V
hereof.  Further, this Section 10.1 shall not under any circumstances permit,
cause or result in delays in the aggregate of more than 365 days.


                                   ARTICLE XI
                                    NOTICES

         11.1    NOTICES.  All notices, requests, demands and other
communications under this Agreement or in connection therewith to be effective
shall be in writing in English and unless otherwise expressly provided herein
shall be deemed to have been duly given or made (i) on the date delivered in
person; (ii) on the date transmitted by facsimile if confirmation is sent first
class U.S. mail within one (1) day; (iii) on the date received if sent by first
class U.S.  mail, Federal Express or other nationally recognized overnight
carrier service or overnight express U.S. mail with service charges or postage
prepaid; in each case (except for personal delivery) such notices, requests,
demands or other communications shall be sent to a Party at its address or
facsimile number as follows, or as otherwise designated by the Party by notice
in accordance herewith:

ILEX:                                      ILEX Oncology
                                           11550 IH 10 West, Suite 300
                                           San Antonio, Texas 78230
                                           Attention:  Richard Love
                                           Telephone Number:  210/949-8200
                                           FAX Number:  210/949-8227



                                     -19-
<PAGE>   24
TBI:                                       The Burnham Institute
                                           1091 North Torrey Pines Road
                                           La Jolla, California 942037
                                           Attention:  Louis Coffman
                                           Telephone Number:  616/646-3100
                                           FAX Number:  616/646-3199


                                  ARTICLE XII
                    WARRANTIES, REPRESENTATION AND INDEMNITY

         12.1    RIGHT TO GRANT AND COMPLETE RIGHTS.  TBI represents and
warrants that it has the legal right to grant the licenses set forth in this
Agreement and by granting such licenses, TBI will not breach any existing
contract, relationship or agreement related to the Technology and/or the Telios
Technology.  TBI represents and warrants that the Technology and Telios
Technology are free of any encumbrance, including, without limitation, claims,
licenses and prior agreements, which would in any way impair the rights granted
to ILEX herein.  TBI represents and warrants that ILEX's exercise of the rights
granted herein will not infringe the Telios Technology.  TBI represents and
warrants that to the best of its knowledge ILEX's exercise of its rights
hereunder will not infringe the patent or other intellectual property rights of
Third Parties.  TBI represents and warrants that SCHEDULE 1.31 is a complete
list of all existing patents and patent applications licensed to or owned by
TBI which relate to THP, Compounds and/or Products.  TBI represents and
warrants that SCHEDULE 1.44 is a complete list of all existing patents and
patent applications licensed to or owned by TBI which relate to THP, Compounds
and/or Products.

         12.2    AUTHORIZATION.  Each Party represents and warrants to the
other Party that it is duly organized and has the authority to operate where it
does business and its execution, delivery, and performance of this Agreement
and the consideration set forth in this Agreement have been duly authorized by
all necessary corporate action and that this Agreement is not in conflict with
any other agreements to which it is Party.

         12.3    COMPLIANCE WITH APPROPRIATE LAW.  Each Party warrants that it
shall comply with any applicable international, national or local laws and
regulations related to the subject matter of this Agreement and that a Party
shall indemnify and hold harmless the other Party from actions related to a
Party's violation of such laws and regulations to the extent permitted by law.

         12.4    RESPONSIBILITY FOR COMPLIANCE.  Each Party shall be, as to its
own activities, responsible for compliance with laws applicable to any sale,
manufacture or other use involving the Technology or Product, including,
without limitation, any applicable export control laws.



                                     -20-
<PAGE>   25


         12.5    LIMITED LIABILITY.

         NOTWITHSTANDING ANYTHING ELSE IN THIS AGREEMENT OR OTHERWISE, NEITHER
ILEX NOR TBI WILL BE LIABLE WITH RESPECT TO ANY SUBJECT MATTER OF THIS
AGREEMENT UNDER ANY CONTRACT, NEGLIGENCE, STRICT LIABILITY OR OTHER LEGAL OR
EQUITABLE THEORY FOR (i) ANY INCIDENTAL, CONSEQUENTIAL OR PUNITIVE DAMAGES OR
LOST PROFITS OR (ii) COST OF PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY OR
SERVICES.

         12.6    WARRANTY INDEMNITY.  Each Party agrees to indemnify and hold
the other Party and its directors, officers, trustees, employees, agents and
representatives, harmless from any liabilities, costs and expenses (including
attorney's fees and expenses), obligations or causes of action arising out of
or related to any breach of the covenants, representations and warranties made
by such Party herein.

         12.7    ILEX GENERAL INDEMNITY.  ILEX agrees to protect, defend,
indemnify and hold TBI and its directors, officers, trustees, employees, agents
and representatives harmless from and against, and to pay any and all losses,
liabilities, claims, demands, causes of action, lawsuits, or other proceedings
(whether in contract, tort, strict liability or otherwise), fines, assessments,
damages or any other amounts of whatever nature which TBI, its directors,
officers, trustees, employees, agents and representatives may sustain or incur,
including all attorney's fees and court costs, as a consequence of any third
Party's (including, but not limited to, ILEX's officers, directors, employees,
agents, consultants, representatives or servants) claims and demands arising
from the use, testing, operation, sale or manufacture of the Technology, or
Products by ILEX or its sub-licensees to the extent such liability is not due
to TBI's gross negligence or intentional misconduct and on the following
conditions:

                 (i)      TBI will promptly notify ILEX in writing of notice of
                          any claims or the commencement of any action, if a
                          claim in respect thereof is to be made against ILEX
                          under SECTION 12.7 ("INDEMNITY CLAIM").

                 (ii)     ILEX shall have the right to, and upon written notice
                          to TBI shall, assume primary responsibility for
                          managing the defense of any claim, action, suit or
                          proceeding brought against TBI that involves an
                          Indemnity Claim, in which event TBI shall cooperate
                          fully with ILEX in such defense, TBI shall take no
                          action which, or fail to take some action the
                          omission of which, might compromise the rights of
                          ILEX under this Agreement.

                 (iii)    ILEX, at its discretion, may settle any such
                          Indemnity Claim at its sole cost and expense in any
                          manner that does not compromise the rights of TBI
                          under this Agreement with respect to the Technology.



                                     -21-
<PAGE>   26

         Provided, ILEX shall not be obligated to indemnify TBI for any claim
or demand of infringement, misuse, misappropriation, theft or breach of
confidence of proprietary rights asserted by a Third Party if such claim or
demand arises from ILEX's exercise of its rights granted herein.

         12.8    TBI GENERAL INDEMNITY. In the event TBI exercises its Grant
Back Rights, TBI agrees to protect, defend, indemnify and hold ILEX and its
directors, officers, trustees, employees, agents and representatives harmless
from and against, and to pay any and all losses, liabilities, claims, demands,
causes of action, lawsuits, or other proceedings (whether in contract, tort,
strict liability or otherwise), fines, assessments, damages or any other
amounts of whatever nature which ILEX, its directors, officers, trustees,
employees, agents and representatives may sustain or incur, including all
attorney's fees and court costs, as a consequence of any Third Party's
(including, but not limited to, TBI's officers, directors, employees, agents,
consultants, representatives or servants) claims and demands arising from the
use, testing, operation, sale or manufacture of the Technology, or Products by
TBI or its sub-licensees to the extent such liability is not due to ILEX's
gross negligence or willful misconduct and on the following conditions:

                 (i)      ILEX will promptly notify TBI in writing of notice of
                          any claims or the commencement of any action, if a
                          claim in respect thereof is to be made against TBI
                          under SECTION 12.8 ("ILEX INDEMNITY CLAIM").

                 (ii)     TBI shall have the right to, and upon written notice
                          to ILEX shall, assume primary responsibility for
                          managing the defense of any claim, action, suit or
                          proceeding brought against ILEX that involves an ILEX
                          Indemnity Claim, in which event ILEX shall cooperate
                          fully with TBI in such defense, ILEX shall take no
                          action which, or fail to take some action the
                          omission of which, might compromise the rights of TBI
                          under this Agreement.

                 (iii)    TBI, at its discretion, may settle any such ILEX
                          Indemnity Claim at its sole cost and expense in any
                          manner that does not compromise the rights of ILEX
                          under this Agreement with respect to the Technology.

         12.9    SURVIVAL.  The indemnities and warranties of this ARTICLE XII
shall survive the termination or expiration of this Agreement.

         12.10   DISCLAIMER.  EXCEPT AS OTHERWISE SPECIFIED HEREIN, TBI
DISCLAIMS ALL WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING, WITHOUT LIMITATION,
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, VALIDITY OF PATENT RIGHTS,
NON- INFRINGEMENT, SAFETY, EFFICIENCY OF TECHNOLOGY OR COMMERCIAL VIABILITY OF
TECHNOLOGY.



                                     -22-
<PAGE>   27

         12.11   INSURANCE.  During the term of this Agreement, ILEX shall
maintain in full force and effect a policy or policy of general liability
insurance and product liability insurance.  Such policies shall name TBI as an
additional insured Party.

                                  ARTICLE XIII
                               DISPUTE RESOLUTION

         13.1    DISPUTE RESOLUTION.  If a dispute arises out of or relates to
this Agreement or its breach (the "MATTER"), the Parties agree to resolve the
Matter as follows:

                 (a)      A Party shall submit written notice of the Matter to
                          the other party and request negotiation;

                 (b)      The Parties shall attempt in good faith to resolve
                          any Matter arising out of or relating to this
                          Agreement promptly by negotiation between
                          representatives, who have the power to settle the
                          Matter, which the Parties may appoint; and

                 (c)      If the Matter has not been resolved within sixty (60)
                          days after a Party's request for negotiation, either
                          Party may request that the Matter be submitted to a
                          sole mediator selected by the Parties for a mandatory
                          one (1) day mediation;

                 (d)      If the Matter has not been resolved by such mediation
                          within thirty (30) days after the Party's request for
                          mediation, then either Party may submit the Matter
                          for binding arbitration by a single, neutral
                          arbitrator, in accordance with the Commercial Rules
                          of the American Arbitration Association ("AAA").  The
                          arbitrator shall be selected from the AAA's large
                          complex case panel, provided, however, if this panel
                          is of insufficient size to pick the arbitrator, then
                          the regular commercial panel shall be used to pick
                          the arbitrator.  The award shall be made within six
                          (6) months of selection of the arbitrator.

         If TBI requests the mediation and/or arbitration, it shall be held in
San Antonio, Texas.  If ILEX requests the mediation and/or arbitration, it
shall be held in San Diego, California.  The Parties, their representatives,
the mediator and the arbitrator shall hold the existence, content and results
of any negotiation, mediation or arbitration in confidence unless disclosure is
required by law or regulation, and in such case the Parties shall take
reasonable precautions to only disclose what is required by law or governmental
regulation.  The arbitrator shall decide the Dispute in accordance with the
applicable laws and the factual evidence presented to the arbitrator.  Any
award of the



                                     -23-
<PAGE>   28

Arbitration shall be binding on the Parties and shall be enforceable in any
court having jurisdiction over the party from whom enforcement is requested.

                                  ARTICLE XIV
                                 MISCELLANEOUS

         14.1    SEVERABILITY.  Any provision of this Agreement that is
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof or affecting the validity or
enforceability of such provision in any other jurisdiction.

         14.2    ENTIRE AGREEMENT.  This Agreement sets forth the entire
agreement and understanding between the Parties as to the subject matter of the
Agreement, and merges and supersedes all prior discussions, proposals, offers
and agreements, if any, with respect to the subject matter of this Agreement.

         14.3    LIMITATION OF AUTHORITY.  Nothing in this Agreement shall be
deemed to make either Party the agent or partner of the other or to create a
partnership or joint venture between the Parties.  Neither ILEX nor TBI shall
have any authority arising out of this Agreement to create any implied or
express liability or obligation in the name or on behalf of the other Party,
and neither Party shall enter into any contract with any person or entity that
purports to bind the other Party.

         14.4    CHOICE OF LAW.  This Agreement shall be deemed accepted and
delivered in and governed by and construed under the laws of the State of
California and the United States of America.  No conflicts of law rule or law
which may refer to the laws of another state, republic or country shall be
considered.  The Parties consent to the jurisdiction and venue of the federal
and state courts located in Bexar County, Texas and San Diego County,
California, concerning any disputes or claims arising from or connected to this
Agreement and agree that any action concerning any disputes or claims from or
connected to this Agreement shall, to the extent not covered by arbitration as
provided for in ARTICLE XIII hereof, be conducted solely within the courts
situated therein.  The Parties hereby exclude the application of The Convention
for the International Sale of Goods.

         14.5    NO WAIVER.  The failure of any Party to enforce or demand
performance of any term of this Agreement shall not be deemed a wavier of any
said term or right.  A waiver may only be executed in writing and signed by the
Party granting such waiver.

         14.6    ASSIGNMENT.  Neither Party may assign this Agreement without
the prior written consent of the other Party, which consent will not be
unreasonably withheld; except, however either Party may assign this Agreement
without such consent to a purchaser of the entire business associated with this
Agreement.


                                     -24-
<PAGE>   29

         14.7    BINDING AGREEMENT.  This Agreement is binding upon and shall
inure to the benefit the legal representatives, administrators, successors,
licensees, and permitted assigns, of ILEX or TBI.

         14.8    COUNTERPARTS.  This Agreement may be executed in any number of
counterparts, each of which shall be deemed an original but all of which
together shall constitute one and the same instrument.  A Party's signature may
be transmitted by facsimile, thereby constituting a signed and delivered
document.

         14.9    HEADINGS.  The headings contained in this Agreement are for
convenience of reference only and shall not be considered in construing this
Agreement.

         14.10   PROHIBITION OF USE OF NAMES.  Neither ILEX nor TBI shall use
the other's name without the other's prior written consent, except as required
by law or governmental regulation; provided, ILEX may identify TBI as the
licensor of the Technology and/or Telios Technology.

         14.11   PATENT MARKING.  The Parties shall comply with applicable
patent marking laws.

         14.12   RESPONSIBILITY FOR EXPENSES.  Each Party is responsible for
its own expenses related to the execution of this Agreement.

         14.13   AMENDMENTS.  No amendment or modification to this Agreement is
effective unless in writing and signed by the Parties.

         14.14   PUBLICITY.  Neither Party shall use the name of the other
Party in any publicity, news release or advertisement related to this Agreement
without the advanced written permission of the other Party; provided, ILEX may
identify TBI as the licensor of the Technology and/or Telios Technology in any
advertisement, solicitation, publication or report.

         14.15   INFORMED REVIEW.  Each Party acknowledges that it and its
counsel have received and reviewed this Agreement and that normal rules of
construction, to the effect that ambiguities are to be resolved against the
drafting Party, shall not apply to this Agreement or to any amendments,
modifications, exhibits or attachments to this Agreement.



                                     -25-
<PAGE>   30

         IN WITNESS WHEREOF, the Parties hereto have executed and delivered
this Agreement in multiple originals by their duly authorized officers and
representatives on the respective dates shown below but effective as of the
Effective Date.

ILEX ONCOLOGY                                THE BURNHAM INSTITUTE
                                  
                                  
                                  
By: /s/ RICHARD LOVE                         By: /s/ ILLEGIBLE
   ---------------------------------            -------------------------------
        Richard Love              
                                  
Title:  President                            Title:                           
                                                   ----------------------------
                                  
Date:   3/27/98                              Date:    3/27/98
     -------------------------------               ----------------------------





                                     -26-