Exhibit 99.1

                                   CERTIFICATE
                                 furnished under
                  Section 906 of the Sarbanes-Oxley Act of 2002


     In connection with the accompanying Annual Report of the Ameren Corporation
Savings Investment Plan (the "Plan") on Form 11-K for the year ended December
31, 2002 as filed with the Securities and Exchange Commission (the "Report"), I,
Donna K. Martin, Vice President, Human Resources, of Ameren Services Company,
the administrator of the Plan, hereby certify, pursuant to 18 U.S.C. Section
1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that
to the best of my knowledge:

(1)  The Report fully complies with the requirements of 13(a) or 15(d) of the
     Securities Act of 1934; and

(2)  The information contained in the Report fairly presents, in all material
     respects, the financial condition and results of operations of the Plan.

     A signed original of this written statement required by Section 906 has
been provided to Ameren Corporation and will be retained by Ameren Corporation
and furnished to the Securities and Exchange Commission or its staff upon
request.

                                                /s/ Donna K. Martin
                                                -----------------------------
                                                Donna K. Martin
                                                Vice President, Human Resources
                                                Ameren Services Company
                                                (Plan Administrator)


Date:  June 30, 2003