Exhibit 99.1





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

     I,  Charles W.  Mueller,  chief  executive  officer of Ameren  Corporation,
hereby  certify that to the best of my  knowledge,  the  accompanying  Report of
Ameren  Corporation  on Form 10-Q for the  quarter  ended  March 31,  2003 fully
complies  with the  requirements  of  Section  13(a) or 15(d) of the  Securities
Exchange  Act of 1934 and  that  information  contained  in such  Report  fairly
presents,  in all material  respects,  the  financial  condition  and results of
operations of Ameren Corporation.



                                            /s/ Charles W. Mueller
                                            ------------------------------------
                                            Charles W. Mueller
                                            Chairman and Chief Executive Officer
                                            (Principal Executive Officer)


Date:  May 14, 2003



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.