SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549



                                    FORM 8-K


                                 CURRENT REPORT




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



                Date of Report (Date of earliest event reported):
                                 March 23, 2004



                  Exact Name of Registrant as specified
                  in its charter;
Commission        State of Incorporation;                     IRS Employer
File Number       Address and Telephone Number                Identification No.
-----------       ----------------------------                ------------------

1-14756           Ameren Corporation                               43-1723446
                  (Missouri Corporation)
                  1901 Chouteau Avenue
                  St. Louis, Missouri 63103
                  (314) 621-3222

1-2967            Union Electric Company                           43-0559760
                  (Missouri Corporation)
                  1901 Chouteau Avenue
                  St. Louis, Missouri 63103
                  (314) 621-3222

1-3672            Central Illinois Public Service Company          37-0211380
                  (Illinois Corporation)
                  607 East Adams Street
                  Springfield, Illinois 62739
                  (217) 523-3600

333-56594 Ameren Energy Generating Company 37-1395586 (Illinois Corporation) 1901 Chouteau Avenue St. Louis, Missouri 63103 (314) 621-3222 2-95569 CILCORP Inc. 37-1169387 (Illinois Corporation) 300 Liberty Street Peoria, Illinois 61602 (309) 677-5230 1-2732 Central Illinois Light Company 37-0211050 (Illinois Corporation) 300 Liberty Street Peoria, Illinois 61602 (309) 677-5230

ITEM 5. OTHER EVENTS AND REGULATION FD DISCLOSURE. On March 23, 2004, Ameren Corporation ("Ameren") entered into an amendment (the "First Amendment") to the Stock Purchase Agreement, dated as of February 2, 2004, among Ameren, Dynegy Corporation ("Dynegy") and certain subsidiaries of Dynegy, setting forth the terms and conditions pursuant to which Ameren will acquire Illinois Power Company ("IPC"), a subsidiary of Dynegy, and Dynegy's 20 percent interest in Electric Energy, Inc. The Stock Purchase Agreement is included as an exhibit to the registrant's Form 8-K filed on February 3, 2004. The First Amendment modifies certain schedules and certain ancillary agreements to the Stock Purchase Agreement, and extends the period for certain pre-closing actions to be taken by the parties. In addition, on March 24, 2004, Ameren and IPC jointly filed with the Illinois Commerce Commission their request for expedited review and approval of the transactions contemplated by the Stock Purchase Agreement, as amended by the First Amendment. The acquisition is also subject to the approval of the Federal Energy Regulatory Commission, the Securities and Exchange Commission, the Federal Communications Commission and to the expiration of the waiting period under the Hart-Scott-Rodino Act. The remaining regulatory filings are expected to be made within the next several weeks. Included as Exhibit 2.1 is the text of the First Amendment, which is incorporated herein by reference. ITEM 7. FINANCIAL STATEMENTS, PRO FORMA FINANCIAL INFORMATION AND EXHIBITS. (a) Not applicable (b) Not applicable (c) The following exhibits are included with this Report: Exhibit No. Description -------- ----------- 2.1 Amendment No. 1 to Stock Purchase Agreement, dated as of March 23, 2004, among Ameren, Dynegy, Illinova Corporation and Illinova Generating Company. The combined Form 8-K is being filed separately by Ameren, Union Electric Company, Central Illinois Public Service Company, Ameren Energy Generating Company, CILCORP Inc. and Central Illinois Light Company (Registrants). Information contained herein relating to any individual registrant has been filed by such registrant on its own behalf. No registrant makes any representation as to information relating to any other registrant.

SIGNATURES Pursuant to the requirements of the Exchange Act, each registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized. The signature for each undersigned company shall be deemed to relate only to matters having reference to such company or its subsidiaries. AMEREN CORPORATION (Registrant) /s/ Martin J. Lyons ------------------------------ Martin J. Lyons Vice President and Controller (Principal Accounting Officer) UNION ELECTRIC COMPANY (Registrant) /s/ Martin J. Lyons ------------------------------ Martin J. Lyons Vice President and Controller (Principal Accounting Officer) CENTRAL ILLINOIS PUBLIC SERVICE COMPANY (Registrant) /s/ Martin J. Lyons ------------------------------ Martin J. Lyons Vice President and Controller (Principal Accounting Officer) AMEREN ENERGY GENERATING COMPANY (Registrant) /s/ Martin J. Lyons ------------------------------ Martin J. Lyons Vice President and Controller (Principal Accounting Officer)

CILCORP Inc. (Registrant) /s/ Martin J. Lyons ------------------------------ Martin J. Lyons Vice President and Controller (Principal Accounting Officer) Central Illinois Light Company (Registrant) /s/ Martin J. Lyons ------------------------------ Martin J. Lyons Vice President and Controller (Principal Accounting Officer) Date: March 24, 2004

Exhibit Index Exhibit No. Description ----------- ----------- 2.1 Amendment No. 1 to Stock Purchase Agreement, dated as of March 23, 2004, among Ameren, Dynegy, Illinova Corporation and Illinova Generating Company.

                                                                     Exhibit 2.1


                               AMENDMENT NO. 1 TO
                            STOCK PURCHASE AGREEMENT


         THIS AMENDMENT NO. 1, dated as of March 23, 2004, to the STOCK PURCHASE
AGREEMENT, dated as of February 2, 2004, is entered into by and among Ameren
Corporation, a Missouri corporation ("Purchaser"), Illinova Corporation, an
Illinois corporation ("Seller"), Illinova Generating Company, an Illinois
corporation ("IGC"), and Dynegy Inc., an Illinois corporation ("Dynegy").
Dynegy, IGC and Seller are referred to herein as the "Dynegy Parties".

                              W I T N E S S E T H:

         WHEREAS, Purchaser and the Dynegy Parties entered into a Stock Purchase
Agreement, dated February 2, 2004 (the "Original Agreement"), providing for the
sale to Purchaser of all of the capital stock of Illinois Power Company, an
Illinois corporation, held by Seller, and IGC's 20% share of Electric Energy,
Inc., an Illinois corporation; and

         WHEREAS, Purchaser and the Dynegy Parties wish to amend the Original
Agreement as set forth herein;

         NOW, THEREFORE, in consideration of the premises and the mutual terms,
conditions and agreements set forth herein, the parties hereto hereby agree as
follows:

                  Section 1 Defined Terms. All capitalized terms used and not
         defined herein have the meanings set forth in the Original Agreement.

                  Section 2  Amendments to Section 1.1.

                           A. The definition of "Ancillary Agreements" included
                  in Section 1.1 of the Original Agreement is amended to add the
                  following after the reference to the "Tier 2 Memorandum,":

                           "the Interim PPA Rider,".

                           B. Section 1.1 of the Original Agreement is amended
                  to add the following definition after the definition of
                  Intercompany Note:

                           ""Interim PPA Rider" means the agreement between DMG
                  and IPC in the form of Exhibit I, with such changes as may be
                  required by Governmental Authorities as a condition to
                  approving the transactions or any portion thereof contemplated
                  by this Agreement and the Ancillary Agreements that are
                  required to be accepted by Seller or by Purchaser, pursuant to
                  the provisions of Section 5.3 or are otherwise accepted by
                  Seller and by Purchaser.".

                  Section 3 Amendment to Section 5.21. Section 5.21(b) of the
         Original Agreement is amended by changing the reference to "30 days" in
         the second sentence to "90 days".

Section 4 Amendment to Section 8.2(j). Section 8.2(j) of the Original Agreement is amended by deleting such Section and replacing it with the following: "Solely if the Closing occurs after September 10, 2004, the Tilton Assets, or IPC's rights, interests, assets, liabilities and obligations with respect to the electric generating equipment and real estate at the Tilton Energy Center, shall have been transferred to DMG and IPC shall have no remaining obligations with respect to the Tilton Assets. For avoidance of doubt, it is the intent of this Section 8.2(j) that all of IPC's rights, interest, assets, liabilities and obligations with respect to the Tilton Assets, or IPC's rights, interests, assets, liabilities and obligations with respect to the electric generating equipment and real estate at the Tilton Energy Center, shall have been transferred to or otherwise come to be held by DMG, excluding only those rights, interests, assets, liabilities and obligations of IPC as a public utility that are necessary for the continued operation by DMG of the Tilton Energy Center, including IPC's rights, interests, assets, liabilities and obligations under the Interconnection Agreement and the gas service contracts listed on Schedule 3.19. Nothing herein shall preclude DMG from acquiring the Tilton Assets, or the electric generating equipment and real estate at the Tilton Energy Center, at any time prior to September 10, 2004." Section 5 Amendment to Schedule 5.3(b). Schedule 5.3(b) to the Original Agreement is amended as set forth in Exhibit 1 hereto. Section 6 Amendment to Schedule 5.15. Schedule 5.15 to the Original Agreement is amended as set forth in Exhibit 2 hereto. Section 7 Amendment to Schedule 8.1(b). Schedule 8.1(b) to the Original Agreement is amended as set forth in Exhibit 3 hereto. Section 8 Amendment to Schedule 8.2(b). Schedule 8.2(b) to the Original Agreement is amended as set forth in Exhibit 4 hereto. Section 9 Amendment to Exhibit B. Exhibit B to the Original Agreement is amended by changing the reference to "thirty (30) days" in the bracketed note at the top of page 1 of Exhibit B to "ninety (90) days". Section 10 Amendment to Exhibit F. Exhibit F to the Original Agreement is amended by replacing the agreement attached as Exhibit F with the Form of Blackstart Agreement attached hereto as Exhibit 5. Section 11 Addition of Exhibit I. The Original Agreement is amended by adding, immediately following Exhibit H, a new Exhibit I containing the form of Interim PPA Rider attached hereto as Exhibit 6. Section 12 No Other Amendments. Except as set forth herein, the Original Agreement remains in full force and effect. -2-

Section 13 Counterparts. This Agreement may be executed in one or more counterparts, and by the parties in separate counterparts, each of which when executed shall be deemed to be an original but all of which taken together shall constitute one and the same agreement. -3-

IN WITNESS WHEREOF, Seller, IGC, Dynegy and Purchaser have caused this Amendment No. 1 to the Original Agreement to be executed as of the date first written above by their respective officers thereunto duly authorized. ILLINOVA CORPORATION By: /s/ Robert T. Ray -------------------------------- Name: Robert T. Ray Title: Senior Vice President & Treasurer ILLINOVA GENERATING COMPANY By: /s/ Robert T. Ray -------------------------------- Name: Robert T. Ray Title: Senior Vice President & Treasurer DYNEGY INC. By: /s/ Robert T. Ray -------------------------------- Name: Robert T. Ray Title: Senior Vice President & Treasurer AMEREN CORPORATION By: /s/ Steven R. Sullivan -------------------------------- Name: Steven R. Sullivan Title: Senior Vice President, Regulatory Policy, General Counsel & Secretary -4-