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                                                                    EXHIBIT 10.3

                             TERMINATION AGREEMENT

     This Termination Agreement dated effective June 30, 1999, is made by and
between ILEX ONCOLOGY, INC., a Delaware corporation ("ILEX"), and PRN RESEARCH,
INC., a Texas corporation ("PRN").

                             W I T N E S S E T H:

     WHEREAS, ILEX and PRN are parties to a Service Agreement (the "Service
Agreement") dated effective June 30, 1997; and

     WHEREAS, ILEX and PRN desire to terminate the Service Agreement;

     NOW, THEREFORE, in consideration of the mutual agreements contained herein,
and other good and valuable consideration, the receipt and sufficiency of which
is hereby acknowledged, ILEX and PRN agree as follows:

1.  ILEX shall issue 629,200 shares of common stock, $.01 par value ("Common
    Stock") to PRN. PRN recognizes that the Common Stock is not being registered
    under the Securities Act of 1933, as amended (the "Securities Act"), in
    reliance upon an exemption from the Securities Act which is predicated, in
    part, on the representations and agreements of PRN set forth in this
    Agreement. PRN represents and warrants to ILEX that it is an "accredited
    investor" as that term is defined in Rule 501(a) of the Rules and
    Regulations promulgated pursuant to the Securities Act, and that the Common
    Stock is being acquired solely for its own account for investment and not
    with a view to, or for offer or resale in connection with, a distribution
    thereof within the meaning of the Securities Act. PRN understands that the
    effect of such representation and warranty is that the Common Stock must be
    held indefinitely unless subsequently registered under the Securities Act or
    an exemption from such registration is available at the time for any
    proposed sale or other transfer thereof. PRN represents that it has
    consulted with its counsel in regard to the Securities Act and that it is
    fully familiar with the circumstances under which it is required to hold the
    Common Stock and the limitations upon the transfer or other disposition
    thereof. PRN acknowledges that ILEX is relying upon the trust and accuracy
    of the foregoing representations and warranties in issuing the Common Stock
    under the Securities Act. PRN agrees to and shall indemnify and hold ILEX
    harmless against all liabilities, costs and expenses, including reasonable
    attorneys' fees, incurred by ILEX as a result of any sale, transfer or other
    disposition by PRN of all or any part of the Common Stock in violation of
    the Securities Act. The certificate representing the Common Stock shall bear
    the following legend:

    "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
    INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
    AMENDED. THESE SECURITIES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF
    SUCH REGISTRATION OR AN EXEMPTION THEREFROM UNDER SAID ACT."

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2.   The Service Agreement and the terms, provisions, covenants and agreements
     contained therein are hereby terminated in all respects, and neither PRN
     nor ILEX have any continuing liabilities or obligations to one another
     under the terms and provisions of the Service Agreement.

3.   The Registration Rights Agreement dated July 9, 1997 by an between PRN and
     ILEX shall continue in full force and existence, and this Termination
     Agreement will not in any manner effect the rights and obligations of
     either ILEX or PRN pursuant to such Registration Rights Agreement.

     IN WITNESS WHEREOF, the parties have caused this Termination Agreement to
be duly executed effective as of the date and year first above written.


                                        ILEX ONCOLOGY, INC.



                                        By: /s/ Michael T. Dwyer
                                           -------------------------------
                                           Name: M. T. Dwyer
                                           Title: Vice President & CFO


                                        PRN RESEARCH, INC.


                                        By: /s/ L. Fred Pounds
                                           --------------------------------
                                           Name: L. Fred Pounds
                                           Title: CFO