SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549



                                   FORM 8-K/A


                                 CURRENT REPORT




     Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934



                Date of Report (Date of earliest event reported):
                                January 31, 2003





                               AMEREN CORPORATION
             (Exact name of registrant as specified in its charter)




        Missouri                       1-14756                   43-1723446
(State or other jurisdiction         (Commission              (I.R.S. Employer
     of incorporation)               File Number)            Identification No.)




                 1901 Chouteau Avenue, St. Louis, Missouri 63103
              (Address of principal executive offices and Zip Code)






       Registrant's telephone number, including area code: (314) 621-3222






ITEM 2.   ACQUISITION OR DISPOSITION OF ASSETS (Amended)

          On  January  31,  2003,  Ameren  Corporation  ("Ameren") filed a  Form
8-K  announcing  the  closing  of the  acquisition  of all  of  the  issued  and
outstanding common stock of CILCORP Inc.  ("CILCORP"),  an Illinois corporation,
from The AES  Corporation,  pursuant to an agreement  dated as of April 28, 2002
(the  "Stock  Purchase  Agreement").  On  February  4, 2003,  Ameren  closed its
acquisition  from  The AES  Corporation  of all of the  issued  and  outstanding
membership  interests of AES Medina Valley Cogen (No. 4), LLC ("Medina Valley"),
pursuant to an agreement  dated as of April 28, 2002 (the  "Membership  Interest
Purchase   Agreement").   As  of  such  acquisition,   Medina  Valley  became  a
wholly-owned  subsidiary of AmerenEnergy  Resources  Company,  which is a direct
subsidiary of Ameren that holds its non rate-regulated operations. Medina Valley
has been named AmerenEnergy Medina Valley Cogen (No. 4), LLC.

ITEM 7.   FINANCIAL STATEMENTS AND EXHIBITS (Amended)

(a)       Financial statements of businesses acquired.  Ameren has completed the
          calculations  that  demonstrate  that CILCORP and Medina Valley do not
          constitute a significant business acquisition as defined in applicable
          SEC rules.  Accordingly,  Ameren is not  required to provide  separate
          financial  statements  for  CILCORP  or Medina  Valley.  Historically,
          CILCORP  filed  periodic  reports with the SEC under File No.  1-8946.
          Such reports are available from the public  reference room of the SEC,
          at www.sec.gov and other sources.

(b)       Pro forma financial information. Ameren has completed the calculations
          that  demonstrate  that CILCORP and Medina Valley do not  constitute a
          significant  business  acquisition as defined in applicable SEC rules.
          Accordingly,  Ameren is not  required to provide  pro forma  financial
          information relating to the acquisition of CILCORP or Medina Valley.



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                                    SIGNATURE

     Pursuant to the  requirements  of the Securities  Exchange Act of 1934, the
Registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned thereunto duly authorized.

                                                  AMEREN CORPORATION
                                                     (Registrant)


                                          By     /s/ Martin J. Lyons
                                            ------------------------------------
                                          Name:      Martin J. Lyons
                                          Title: Vice President and Controller
                                                 (Principal Accounting Officer)


Date:  March 7, 2003




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