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                                                                EXHIBIT 10.20(c)


                              AGREEMENT MEMORANDUM

RPR and Introgen agree as follows (all Section references are to the
Collaboration Agreement):

     1.   RPR hereby elects under Section 6.1 to proceed with Later Stage
          Clinical Development and commercialization of INGN 201 (Ad5CMV-p53).

     2.   Introgen shall immediately [*] to [*] INGN 201, as contemplated in
          Section 2.3.3.

     3.   With respect to supply of INGN 201:

               o    Introgen shall use [*] the quantities of INGN 201 clinical
                    materials, according to the schedule, in Exhibit A, which
                    shall be used solely for clinical trials in the RPRP
                    Territory and North America. The price of such materials
                    shall be as per Section 12.3.2 (Ex Works). RPR and Introgen
                    shall [*] as contemplated in Section 12.5.

               o    Introgen and RPR shall supply to each other the quantities
                    of INGN 201 [*], according to the schedule, specified in
                    Exhibit B. The transfer price shall be [*]. [*]

               o    RPR acknowledges that Introgen has the exclusive right under
                    Section 12.3 to manufacture, or have a third party
                    manufacture, and supply Collaboration Products for both
                    clinical trials and commercial sale in North America, and
                    that this right is a fundamental benefit to Introgen under
                    the Collaboration Agreement; RPR agrees [*].



         [*]    Certain information on this page has been omitted and filed
                separately with the Commission. Confidential treatment has been
                requested with respect to the omitted portions.

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                    [*]

                    [*]


               o    RPR and Introgen agree to use their respective best efforts
                    to collaborate with and assist one another on a reciprocal
                    basis to ensure the supply of Collaboration Product for use
                    in North America and the RPRP Territory; provided that such
                    commitment [*] subject in each case to Article 12 of the
                    Collaboration Agreement.

               o    [*]

               o    [*]

     4.   Introgen shall file immediately with the U.S. FDA the [*] package.

All capitalized terms shall have the meaning in the Collaboration Agreement (p53
Products) dated October 7, 1994. References to "RPR" include RPRP. This
agreement shall terminate upon a termination of the Collaboration, except that
RPR's obligation to purchase the materials in Exhibit A shall survive any such
termination. This Agreement Memorandum is effective as of July 22, 1997.

INTROGEN THERAPEUTICS, INC.                     RHONE POULENC RORER
                                                PHARMACEUTICALS, INC.

BY: /s/ James W. Albrecht, Jr.                  BY: /s/ Christine A. Jacobs
   ---------------------------                     ------------------------


         [*]    Certain information on this page has been omitted and filed
                separately with the Commission. Confidential treatment has been
                requested with respect to the omitted portions.



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