<PAGE>   1
                                                                   EXHIBIT 10.61

                          CONSULTING SERVICES AGREEMENT

                                     BETWEEN

                               ILEX ONCOLOGY, INC.

                                       AND

                            DANIEL D. VON HOFF, M.D.


         THIS CONSULTING SERVICES AGREEMENT (the "Agreement") is made and
entered into as of the 1st day of July, 1997 (the "Effective Date") by and
between ILEX Oncology, Inc., a Delaware corporation ("ILEX"), and Daniel D.
Von Hoff, M.D., an individual residing in San Antonio, Texas ("Dr. Von Hoff").

         IN CONSIDERATION of the mutual agreements herein contained and other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, it is agreed as follows:

         1.0 Prior Agreement Superseded. ILEX and Dr. Von Hoff have entered into
that one certain Consulting Services Agreement (the "Consulting Services
Agreement") dated January 1, 1995. The parties agree that this Agreement
supersedes the Consulting Services Agreement in its entirety.

         2.0 Engagement. ILEX hereby engages Dr. Von Hoff to serve as a
consultant to ILEX, and Dr. Von Hoff hereby accepts such engagement, upon and
subject to the terms and conditions set forth herein. Dr. Von Hoff currently
serves as Director of the Institute for Drug Development ("IDD"), a division of
the CTRC Research Foundation ("CTRC"), as Director of CTRC and as Director of
Research for Physician Reliance Network, Inc. ("PRN"). To the extent that those
engagements require approvals for this Agreement, Dr. Von Hoff shall be
primarily responsible for securing the same, with the assistance of ILEX. This
Agreement is expressly conditional upon obtaining such approvals, and shall
terminate if such approvals cannot be obtained within a reasonable period of
time after the Effective Date.

         3.0 Affiliations. From and following the Effective Date of this
Agreement, Dr. Von Hoff shall not act as a consultant for any person or entity
other than ILEX except through ILEX Advisory Services. Notwithstanding the
foregoing, Dr. Von Hoff may serve (a) as Director of the IDD and CTRC as set
forth in Section 2.0 and (b) on scientific advisory boards for other persons or
entities in addition to those set forth in Section 2.0, provided that (i) such
affiliation(s) would not conflict with his duties and responsibilities hereunder
and (ii) Dr. Von Hoff has obtained the prior written consent of the Chief
Executive Officer of ILEX. Dr. Von Hoff warrants and represents to ILEX that 



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Dr. Von Hoff has no affiliations in any capacity with any persons or entities
other than ILEX, except those listed on Schedule 3.0 attached hereto.

         4.0 Duties. Dr. Von Hoff agrees to provide the services set forth on
Exhibit A which is incorporated herein for all purposes. The parties understand
and acknowledge that potential conflicts or duality of interest, or the
appearance of such conflict or duality of interest, may arise during Dr. Von
Hoff's performance of those duties and services as a result of Dr. Von Hoff's
other affiliations. Both parties recognize the importance of avoiding both
actual conflicts and the appearance of conflicts of interest. The parties will
therefore mutually develop procedures for identifying and evaluating actual,
potential and apparent conflicts of duality of interests. In discharging his
duties and responsibilities hereunder, Dr. Von Hoff will advise ILEX when and if
an actual or potential conflict arises. The parties will then mutually work at
attempting to resolve the conflict.

         5.0 Compensation. Compensation for Dr. Von Hoff's services shall be in
accordance with Exhibit B, which is attached hereto and incorporated herein for
all purposes.

         6.0 Independent Contractor. The parties understand and acknowledge that
Dr. Von Hoff is an independent contractor and is not an employee of ILEX for the
purposes of this Agreement, the Social Security Act, the income withholding
provision of the Internal Revenue Code of 1986, as amended, or other federal or
state laws relating to compensation, insurance, unemployment, or workman's
compensation. Dr. Von Hoff acknowledges and agrees that it shall be his
obligation to report as self-employment income all compensation received or
accrued as a result of this Agreement. Dr. Von Hoff acknowledges that he will
not be entitled to any insurance, pension, profit sharing, retirement or other
employee benefits which ILEX may provide to its employees during the term of
this Agreement. This Agreement shall not be construed as creating a partnership,
joint venture, agency or employment relationship, or as granting a franchise
under either federal or state law.

         7.0 Inventions. Dr. Von Hoff warrants and represents to ILEX that Dr.
Von Hoff has no affiliation with any other persons or entities which require, to
any degree or under any conditions, that Dr. Von Hoff assign his rights to any
discoveries, inventions or developments to such persons or entities except as
set forth on Schedule 7.0 attached hereto. In the performance of his duties and
responsibilities hereunder, Dr. Von Hoff may conceive, make or develop products,
processes or other intellectual property. It is the intent of the parties that
intellectual property conceived, made or developed by Dr. Von Hoff during the
performance of his duties and responsibilities hereunder or that is conceived,
made or developed using ILEX's funds, facilities, materials or information,
shall be owned by ILEX. Dr. Von Hoff will ensure that his obligations under
affiliations with any other persons or entities, including, without limitation,
those persons or entities listed in Schedule 7.0, do not extend to intellectual
property rightfully owned by ILEX. Dr. Von Hoff will assist ILEX in obtaining
legal protection for such intellectual property as part of his duties and
responsibilities hereunder, and will execute such documents as reasonably
necessary to secure such protection and confirm ownership in ILEX.

                                      -2-

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         8.0 Confidential Information. Dr. Von Hoff agrees to maintain in
confidence all information and materials provided by, or obtained from or
through, ILEX including, without limitation, all information regarding drugs;
pharmaceuticals; gene manipulations and/or therapy; products, compounds and
compositions resulting from chemical, rDNA, genetic engineering or other
methods; potential new uses of existing drugs, compounds or compositions;
medical devices; and all financial information, computer software and
documentation; and other information relating to the business of ILEX
(collectively, the "Confidential Information"). Dr. Von Hoff shall not publish,
use or disclose Confidential Information learned, developed or acquired as a
result of services offered under this Agreement without ILEX's prior written
consent. Confidential Information shall not include (i) information which was
rightfully in Dr. Von Hoff's possession without an obligation of confidentiality
prior to disclosure by or through ILEX; (ii) information which lawfully becomes
part of the public knowledge, literature or generally available to the public
through no act of Dr. Von Hoff; or (iii) information obtained from any third
party, provided that any such third party did not obtain such information from
ILEX or obtain such information in confidence. Dr. Von Hoff shall protect the
Confidential information and shall take all reasonable steps to prevent the
unauthorized disclosure, dissemination, or publication of the Confidential
Information.

         All data, records, analyses, reports and material prepared or complied
by Dr. Von Hoff or furnished to Dr. Von Hoff, in connection with this Agreement
during the term hereof shall be the sole and exclusive property of ILEX, and all
of such data, records, analyses, reports and materials, and all copies thereof,
shall be delivered to ILEX at its request or on the termination of this
Agreement.

         The parties acknowledge that the terms of Dr. Von Hoff's other
affiliations also contain or require certain obligations of confidentiality. In
discharging his duties relative to Confidential Information, Dr. Von Hoff shall
advise ILEX when and if an actual or potential conflict with such other
obligations arise. The parties will then mutually work at attempting to resolve
the conflict. If such conflict cannot be resolved, Dr. Von Hoff is expressly
excused from performing any services hereunder that would result in a breach or
potential breach of his confidentiality obligations owed to another entity.

         9.0 Term and Termination.

         9.1 Term. Subject to the rights of termination set forth in this
Section 9.0, this Agreement shall remain in full force and effect from July 1,
1997 until June 30, 2002, unless sooner terminated by Dr. Von Hoff's death or
continuing inability to discharge the duties hereunder for three (3) consecutive
months. Ninety (90) days prior to the end of the term of this Agreement, the
parties shall enter into negotiations regarding the renewal of this Agreement or
the execution of a new agreement, which renewal or new agreement shall contain
such terms and conditions as may be agreed by the parties.

                                      -3-

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         9.2 Voluntary Termination. During the term of this Agreement, either
party may terminate this Agreement without cause, by giving 120 days written
notice of termination to the other party.

         9.3 Termination With Cause. In the event of breach of this Agreement by
either party, the non-breaching party may, at its option, cancel this Agreement
for such breach by giving written notice of cancellation to the breaching party,
which cancellation shall be effective thirty (30) days following the delivery of
such notice or such later time as may be specified in such notice, unless the
breaching party shall have cured such breach prior to the expiration of the
notice.

         9.4  Limited Survival Upon Termination. Sections 7.0 and 8.0 shall  
survive termination of this Agreement and shall remain in full force and effect.

        10.0  Miscellaneous.

        10.1  Notices. All notices, requests, demands, and other communications
hereunder shall be in writing and, unless otherwise provided herein, shall be
deemed to have been duly given upon hand delivery or upon deposit in the United
States Mail, postage prepaid, certified or registered mail, return receipt
requested, as follows:

         If to ILEX:

                  ILEX Oncology, Inc.
                  11550 IH 10 West, Suite 300
                  San Antonio, TX  78230-1064
                  Attention:  Richard L. Love

         If to Dr. Von Hoff:

                  Daniel D. Von Hoff, M.D.
                  226 Branch Oak Way
                  San Antonio, Texas 78230

or at such other address as shall have been furnished to the other in writing in
accordance herewith, except that such notice of such change shall be effective
only upon receipt.

        10.2  Amendments and Waiver. This Agreement may be amended or modified
by, and only by, a written instrument executed by all the parties hereto. The
terms of this Agreement may be waived by, and only by, a written instrument
executed by the party against whom such waiver is sought to be enforced.

                                      -4-

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        10.3  Section and Other Headings. The section and other headings
contained in this Agreement are for convenience of reference only and shall not
in any way affect the meaning or interpretation of this Agreement.

        10.4  Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be deemed an original and all of which shall
constitute one and the same instrument.

        10.5  Assignments and Parties in Interest. This Agreement shall inure to
the benefit of and be binding upon the parties hereto and their respective
successors and assigns. This Agreement calls for Dr. Von Hoff's personal
services and may not be assigned by Dr. Von Hoff without the prior written
consent of ILEX.

        10.6  No Implied Rights or Remedies. Except as otherwise expressly
provided herein, nothing herein expressed or implied is intended or shall be
construed to confer upon or to give any person, firm, or corporation, other than
the parties hereto and their respective successors and assigns, any rights or
remedies under or by reason of this Agreement.

        10.7  Agreement of Further Cooperation. Each of the parties agrees to
execute and deliver such further documents and to cooperate in such manner as
may be necessary to implement and give effect to the agreements contained
herein.

        10.8  Entire Agreement. This Agreement, together with all exhibits
hereto, embodies the entire agreement and understanding between the parties
hereto relating to the subject matter hereof and supersedes any prior agreements
and understandings relating to the subject matter hereof.

        10.9  Severability. If any part or provision of this Agreement is or
shall be deemed violative of any applicable laws, rules or regulations, such
legal invalidity shall not void this Agreement or affect the remaining terms and
provisions of this Agreement, and this Agreement shall be construed and
interpreted to comport with all such laws, rules or regulations to the maximum
extent possible.

        10.10 Applicable Law. This Agreement has been accepted and made
performable in Bexar County, Texas. This Agreement and the rights and
obligations of the parties hereto shall be construed under and governed by the
laws of the State of Texas, without giving effect to principles of conflict of
laws. The exclusive venue for resolution of any dispute between the parties
related to the subject matter of this Agreement shall be in Bexar County, Texas.

         EXECUTED as of the day and year first above written.

                                                   ILEX ONCOLOGY, INC.


                                                   By:      
                                                      -------------------------
                                                   Name:    
                                                        -----------------------
                                                   Title:   
                                                         ----------------------
                                                   CONSULTANT:


                                                   ----------------------------
                                                   Daniel D. Von Hoff, M.D.

                                      -5-


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                                    EXHIBIT A


                               DUTIES AND SERVICES


         1.0 Consultation Services. Dr. Von Hoff shall perform the following
services for ILEX. In performing these services, Dr. Von Hoff shall at all times
exercise his independent judgment, discretion and control to accomplish the
stated objective.

             1.1  Clinical Trials Advisory Board. Dr. Von Hoff shall organize 
for the benefit of ILEX a Clinical Trials Advisory Board (the "CTAB") which
shall be composed of such persons as may be appointed by ILEX in consultation
with Dr. Von Hoff. The CTAB shall be organized and operate pursuant to a policy
developed by Dr. Von Hoff and approved by ILEX. The CTAB shall hold at least
four (4) meetings per year, at such time and place as designated by the CTAB.

             1.2  Clinical Trials Advisory Board Chairman. Dr. Von Hoff shall be
a member of the CTAB and serve as chairman of the CTAB. Dr. Von Hoff shall
attend all meetings of the CTAB and in accordance with the terms of this
Agreement report to ILEX the action and recommendations of the CTAB.

             1.3  Scientific Advisory Board Co-Chairman. Dr. Von Hoff shall
be a member of the Scientific Advisory Board (the "SAB"), a committee organized
for the benefit of ILEX, and serve as co-chairman of the committee. The SAB is
composed of such persons appointed by ILEX in consultation with Dr. Von Hoff.
The SAB operates and shall continue to operate pursuant to a policy developed by
Dr. Von Hoff and approved by ILEX. Dr. Von Hoff shall attend all meetings of the
SAB and in accordance with the terms of this Agreement report to ILEX the action
and recommendations of the SAB.

             1.4  Joint Management Board. Dr. Von Hoff shall serve as a member 
of the joint management board (the "JMB") created pursuant to the Research
Agreement dated January 31, 1997 among PRN, IDD and ILEX. Dr. Von Hoff shall
attend all meetings of the JMB and in accordance with the terms of this
Agreement report to ILEX the action and recommendations of the JMB.

             1.4  Drug Acquisition. Dr. Von Hoff shall, consistent with the
terms of this Agreement and in collaboration with the SAB, advise the management
of ILEX of viable opportunities for ILEX to acquire for the purpose of
commercialization chemotherapy compounds and drugs as well as other therapeutic
or supportive care compounds.

             1.5  Network of Clinical Trials Sites. Dr. Von Hoff shall,
consistent with the terms of this Agreement, advise and assist the management of
ILEX in creating a network of clinical trials sites (including, without
limitation, PRN) that can rapidly accrue patients to clinical trials.



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             1.6  Scientific Review. In conjunction with the SAB, Dr. Von
Hoff shall review scientific and clinical data on compounds acquired by ILEX. As
co-chairman of the SAB, Dr. Von Hoff shall report to the management of ILEX the
results of the SAB findings and recommendations relative to such compounds.

             1.7  Clinical Development. Dr. Von Hoff shall, consistent with the 
terms of this Agreement, advise and assist the management of ILEX in
establishing the strategic direction of ILEX's clinical development plans.

             1.8  Strategic Plans. Dr. Von Hoff shall, consistent with the terms
of this Agreement, advise and assist the senior management of ILEX in
formulating plans for the strategic direction of ILEX.

             1.9  Advisory Services. Dr. Von Hoff shall, consistent with the 
terms of this Agreement, advise and assist the management of ILEX in formulating
plans for the development of and in developing ILEX's Advisory Services
business.

             1.10  Presentations. Dr. Von Hoff shall, consistent with the
terms of this Agreement, make presentations for and on behalf of ILEX to
companies regarding ILEX's contract research capabilities and advise and assist
the management of ILEX in meeting ILEX's contract research business goals.
Additionally, Dr. Von Hoff shall consistent with the terms of this Agreement,
make presentations for and on behalf of ILEX to financial investors and/or
potential financial investors regarding ILEX's portfolio of compounds provided
that such presentations shall include an appropriate disclosure of Dr. Von
Hoff's financial relationship with ILEX.

             1.11  Positions. Dr. Von Hoff shall, upon request by ILEX,
serve as the Chief Medical Officer of ILEX and, subject to approval of the
shareholders of ILEX, as a Director of ILEX.

             1.12  Additional Services. In addition to the other services
specified in this Section 1.0, Dr. Von Hoff shall, consistent with the terms of
this Agreement, perform such other services to ILEX as necessary to build
stockholder value in ILEX.

         2.0 Requisites. In providing services under this Agreement, Dr. Von
Hoff shall at all times perform his duties and responsibilities in conformance
with the following requisite standards of conduct:

             2.1 Dr. Von Hoff will not actively participate in final decisions 
regarding the acquisition of technologies or compounds owned or discovered by or
licensed to the IDD, when such actions would constitute a conflict of interest,
give the appearance of a conflict of interest or a breach of any policy of IDD
or ILEX.

                                      A-2

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             2.2   Dr. Von Hoff shall not actively participate in decisions
regarding the acquisition of technologies or compounds for which Dr. Von Hoff
was the Principal Investigator, supervised the Principle Investigator or
provided leadership for the clinical or preclinical studies for such compounds
or technologies, when such actions would constitute a conflict of interest, give
the appearance of a conflict of interest or a breach of any policy of ILEX or
the sponsor of the study.

             2.3   Dr. Von Hoff shall not function as the Principal
Investigator for or supervise the Principal Investigator or clinical or
preclinical studies conducted by ILEX.

             2.4   If Dr. Von Hoff publishes an article, paper or other work
regarding technologies or compounds owned or discovered by ILEX or licensed to
ILEX, Dr. Von Hoff shall make an appropriate disclosure of the fact that he has
a financial interest in ILEX.

                                      A-3

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                                    EXHIBIT B


                                  COMPENSATION


1.       ILEX shall pay to Dr. Von Hoff for Dr. Von Hoff's services a fee equal 
to Two Hundred Forty-Three Thousand and No/100 Dollars ($243,000.00) per year,
which shall be paid in monthly installments of $20,250.00 each commencing on
July 15, 1997. In addition, ILEX shall pay to Dr. Von Hoff each month during
each calendar year an incentive fee equal to the product of (a) a fraction, the
numerator of which is $100,000 and the denominator of which is the annual
revenue target established by the Board of Directors of ILEX (the "Board") for
such calendar year times (b) the actual revenue received by ILEX during the
preceding month; provided, however, the sum of all such incentive fees paid to
Dr. Von Hoff shall not exceed $125,000.00 in any calendar year. The parties
agree that the 1997 annual revenue target is $15,632,000. The Board shall
establish the annual revenue target for each calendar year on or before March
31st of such calendar year; provided, however, in the event that the Board fails
to establish the annual revenue target for any calendar year on or before March
31st of such year, the annual revenue target for such calendar year shall be
deemed to be equal to the annual revenue target for the previous calendar year.
In addition to the fees and incentive fees set forth hereinabove, (i) ILEX shall
reimburse Dr. Von Hoff for all expenses reasonably incurred by Dr. Von Hoff in
connection with the performance of Dr. Von Hoff's responsibilities set forth
herein in accordance with the prevailing practice and policy of ILEX and (ii)
ILEX shall provide a furnished office for Dr. Von Hoff's use in connection with
his performance of his responsibilities set for herein. Notwithstanding any
other provision hereinabove to the contrary, (x) the parties agree to review all
fees payable to Dr. Von Hoff hereunder on the first anniversary date of this
Agreement and on each anniversary date thereafter to determine whether such fees
should be adjusted so as to insure that such fees are consistent with prevailing
industry practices for compensating individuals with skills and experiences
comparable to those of Dr. Von Hoff and (y) in the event Dr. Von Hoff's
consulting agreements with PRN and/or CTRC are modified so that Dr. Von Hoff's
consulting services to PRN and/or CTRC, as the case may be, are reduced and
consequently Dr. Von Hoff's compensation from PRN and/or CTRC, as the case may
be, is reduced, then Dr. Von Hoff agrees to spend an additional amount of time
performing consulting services for ILEX equal to the reduction in consulting
services to PRN and/or CTRC, as the case may be, and ILEX agrees that Dr. Von
Hoff's compensation hereunder shall be increased accordingly in an amount equal
to the reduction in compensation received by Dr. Von Hoff from PRN and/or CTRC,
as the case may be.

2.       Notwithstanding any other provision herein to the contrary, the parties
agree that Dr. Von Hoff acquired the following rights granted under the
Consulting Services Agreement and that Dr. Von Hoff shall retain such rights:

         a.       Right to Purchase Common Stock. Pursuant to the terms of the
                  Consulting Services Agreement, Dr. Von Hoff was entitled to
                  purchase, for a period of thirty (30) days 


<PAGE>   10

                  from the date of Consulting Services Agreement, and did
                  purchase 640,000 shares (the "Shares") of common stock, par
                  value $.01 per share, of ILEX at a price of $.10 per share
                  (the "Purchase Price"), which shares were converted into an
                  aggregate of 365,379 shares pursuant to the reverse stock
                  split effected by ILEX in February 1997.

         b.       Financing. Pursuant to the terms of the Consulting Services 
                  Agreement, ILEX agreed to loan and did loan Dr. Von Hoff 
                  sixty-four thousand dollars ($64,000.00) for the purchase of 
                  the Shares. Such loan was evidenced by a promissory note 
                  dated April 12, 1995 (the "Note") and related agreements as 
                  required by ILEX. The Note bears interest at a rate of eight 
                  percent (8%) simple interest per annum (i.e. not compounded) 
                  (the "Agreed Rate") and is payable in quarterly installments 
                  based upon a ten (10) year amortization schedule and will 
                  mature on January 1, 1999.  The Note is secured by a pledge 
                  of that number of Shares determined by dividing the
                  outstanding principal balance of the Note by the per share 
                  purchase price of the Shares.  The pledge agreement contains 
                  a mechanism for partial releases of pledged shares to reflect
                  reductions in the unpaid balance of the Note.

         c.       Restrictions on Shares. Dr. Von Hoff's ownership of the 
                  Shares is subject to the following restrictions, in addition 
                  to restrictions on transfer that might be imposed by 
                  applicable state or federal securities laws.

                  (1)      For a period of four (4) years from April 12, 1995,
                           the date Dr. Von Hoff purchased the Shares (the
                           "Purchase Date"), Dr. Von Hoff shall not sell,
                           transfer, pledge or otherwise dispose of or encumber
                           the Shares, or any of them, other than as provided in
                           this Agreement.

                  (2)      In the event this Agreement is terminated pursuant to
                           Section 10.11 of the Agreement, during the term
                           hereof for cause by ILEX or without cause by Dr. Von
                           Hoff, ILEX shall have the right, but not the
                           obligation, to purchase the Shares from Dr. Von Hoff;
                           provided, however, that the number of Shares to which
                           such right to purchase applies shall be reduced by
                           25% for each full calendar year which has expired
                           since January 1, 1995 as of the effective date of
                           such termination (the "Termination Date"). The price
                           per share to be paid by ILEX for any Shares purchased
                           by it pursuant to this paragraph shall be equal to
                           the Purchase Price plus interest at the Agreed Rate
                           from the Purchase Date through the Termination Date.

                                      B-2

<PAGE>   11



3.       Stock Option.

         a.       As additional compensation for services rendered under the 
                  Consulting Services Agreement, ILEX granted to Dr. Von Hoff
                  an option to acquire up to 50,000 shares of common stock
                  ("Common Stock") of ILEX, which shares were converted into
                  an aggregate of 28,546 shares of Common Stock pursuant to
                  the reverse stock split effected by ILEX in February 1997.
                  The exercise price of the option was $2.00 per share prior
                  to the reverse stock split ($3.50 per share after the
                  reverse stock split). The option vests over four (4) years
                  as follows: 25% on January 1, 1996, 25% on January 1, 1997,
                  25% on January 1, 1998 and 25% on January 1, 1999. All
                  options must be exercised upon the later of (i) January 1,
                  2000, (ii) one year subsequent to the termination of this
                  Agreement for any reason, by ILEX, or (iii) one year
                  subsequent to the termination of the "lock-up period" that
                  is negotiated by ILEX and its underwriters in connection
                  with an initial public offering of ILEX's Common Stock (the
                  "Option Term"); provided, however, in no event will the 
                  Option Term extend beyond January 1, 2005. The option is 
                  evidenced by a separate instrument dated September 29, 1995.

         b.       The stock option issued to Dr. Von Hoff pursuant to Section 3
                  of Exhibit B of the Consulting Services Agreement was
                  consistent with ILEX's stock option plan (the "Plan") to be
                  adopted for key employees of ILEX. Accordingly, Dr. Von Hoff
                  has the following rights relating to termination of this
                  Agreement pursuant to the provisions of Article 9:

                  (1)      In the event of termination by ILEX without cause
                           under Section 9.2, (i) outstanding stock options held
                           by Dr. Von Hoff which are then vested shall remain
                           exercisable for the Option Term, (ii) if, within ten
                           (10) days of such termination, Dr. Von Hoff notifies
                           ILEX that he is making an election under this
                           Section, outstanding stock options held by Dr. Von
                           Hoff which would vest within one year from the date
                           of termination shall automatically become vested and
                           remain exercisable for the Option Term, and (iii)
                           after giving effect to any accelerated vesting under
                           clause (ii) above, any then unvested portion of Dr.
                           Von Hoff's outstanding stock options shall lapse.

                  (2)      In event of termination by ILEX for "cause" under
                           Section 9.3, upon death or disability of Dr. Von Hoff
                           or by Dr. Von Hoff pursuant to a voluntary
                           resignation under Section 9.2, (i) any portion of Dr.
                           Von Hoff's outstanding stock options which are vested
                           as of the date of termination shall remain
                           exercisable for the Option Term, and (ii) any then
                           unvested portion of Dr. Von Hoff's outstanding stock
                           options shall lapse.



                                      B-3