<PAGE>

                                  UNITED STATES
                       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):
                                   May 1, 2000





                     CENTRAL ILLINOIS PUBLIC SERVICE COMPANY
             (Exact name of registrant as specified in its charter)




          Illinois                   1-3672                       37-0211380
(State or other jurisdiction      (Commission                 (I.R.S. Employer
     of incorporation)            File Number)               Identification No.)




               607 East Adams Street, Springfield, Illinois 62739
              (Address of principal executive offices and Zip Code)






       Registrant's telephone number, including area code: (217) 523-3600


<PAGE>


ITEM 5. OTHER EVENTS

     Reference is made to Item 1. Business under the captions "General", Item 2.
Properties  and  Item 7.  Management's  Discussion  and  Analysis  of  Financial
Condition and Results of Operations  under the caption  "Overview" and "Electric
Industry  Restructuring"  in the  Registrant's  Form  10-K  for the  year  ended
December 31, 1999,  for a discussion  of the  Registrant's  plan to transfer its
electric  generating  facilities  to a new  nonregulated  subsidiary  of  Ameren
Corporation  (Ameren),  the Registrant's  parent company,  pursuant to Illinois'
Electric Service Customer Choice and Rate Relief Law of 1997.

     On May 1, 2000,  following  the receipt of all  required  State and Federal
regulatory approvals,  the Registrant transferred its electric generating assets
and  liabilities  to a  newly  created  nonregulated  affiliate,  Ameren  Energy
Generating Company (Generating Company), a wholly-owned subsidiary of Ameren, in
exchange for a promissory note from Generating  Company in the principal  amount
of approximately $600 million (the net book value of the assets and liabilities)
and  Generating  Company common stock.  The  promissory  note has a term of five
years and bears interest at 7% based on a 10-year amortization.  The transferred
assets  represent  a  generating  capacity  of  approximately  2,900  megawatts.
Approximately  45% of the Registrant's  employees were transferred to Generating
Company as a part of the transaction.

     Also on May 1, 2000,  an electric  power supply  agreement was entered into
between Generating Company and its newly created nonregulated affiliate,  Ameren
Energy  Marketing  Company  (Marketing  Company).  On the same  date,  Marketing
Company  entered into an electric power supply  agreement with the Registrant to
supply it  sufficient  power to meet native load  requirements.  This  agreement
expires December 31, 2004. Power will continue to be jointly  dispatched between
Union Electric Company, another subsidiary of Ameren, and Generating Company.

     The  creation of the new  subsidiaries  and the  transfer  of  Registrant's
generating  assets  and  liabilities  did  not  have a  material  effect  on the
Registrant's financial position, results of operation or liquidity.



                                    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.

                                             CENTRAL ILLINOIS PUBLIC
                                               SERVICE COMPANY
                                                (Registrant)


                                             By    /s/ Warner L. Baxter
                                                 ------------------------
                                                       Warner L. Baxter
                                             Vice President and Controller
                                             (Principal Accounting Officer)

Date: May 5, 2000



                                      -2-
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UNITED STATES
                       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):
                                   May 1, 2000

                     CENTRAL ILLINOIS PUBLIC SERVICE COMPANY
             (Exact name of registrant as specified in its charter)

          Illinois                   1-3672                       37-0211380
(State or other jurisdiction      (Commission                 (I.R.S. Employer
     of incorporation)            File Number)               Identification No.)

               607 East Adams Street, Springfield, Illinois 62739
              (Address of principal executive offices and Zip Code)

       Registrant's telephone number, including area code: (217) 523-3600
ITEM 5. OTHER EVENTS

     Reference is made to Item 1. Business under the captions "General", Item 2.
Properties  and  Item 7.  Management's  Discussion  and  Analysis  of  Financial
Condition and Results of Operations  under the caption  "Overview" and "Electric
Industry  Restructuring"  in the  Registrant's  Form  10-K  for the  year  ended
December 31, 1999,  for a discussion  of the  Registrant's  plan to transfer its
electric  generating  facilities  to a new  nonregulated  subsidiary  of  Ameren
Corporation  (Ameren),  the Registrant's  parent company,  pursuant to Illinois'
Electric Service Customer Choice and Rate Relief Law of 1997.

     On May 1, 2000,  following  the receipt of all  required  State and Federal
regulatory approvals,  the Registrant transferred its electric generating assets
and  liabilities  to a  newly  created  nonregulated  affiliate,  Ameren  Energy
Generating Company (Generating Company), a wholly-owned subsidiary of Ameren, in
exchange for a promissory note from Generating  Company in the principal  amount
of approximately $600 million (the net book value of the assets and liabilities)
and  Generating  Company common stock.  The  promissory  note has a term of five
years and bears interest at 7% based on a 10-year amortization.  The transferred
assets  represent  a  generating  capacity  of  approximately  2,900  megawatts.
Approximately  45% of the Registrant's  employees were transferred to Generating
Company as a part of the transaction.

     Also on May 1, 2000,  an electric  power supply  agreement was entered into
between Generating Company and its newly created nonregulated affiliate,  Ameren
Energy  Marketing  Company  (Marketing  Company).  On the same  date,  Marketing
Company  entered into an electric power supply  agreement with the Registrant to
supply it  sufficient  power to meet native load  requirements.  This  agreement
expires December 31, 2004. Power will continue to be jointly  dispatched between
Union Electric Company, another subsidiary of Ameren, and Generating Company.

     The  creation of the new  subsidiaries  and the  transfer  of  Registrant's
generating  assets  and  liabilities  did  not  have a  material  effect  on the
Registrant's financial position, results of operation or liquidity.

                                    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.

                                             CENTRAL ILLINOIS PUBLIC
                                               SERVICE COMPANY
                                                (Registrant)

                                             By    /s/ Warner L. Baxter
                                                 ------------------------
                                                       Warner L. Baxter
                                             Vice President and Controller
                                             (Principal Accounting Officer)

Date: May 5, 2000

                                      -2-