<PAGE>

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549


                                    FORM 10-Q

[X]  QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
     ACT OF 1934

     For Quarterly Period Ended March 31, 2000

[ ]  TRANSITION  REPORT  PURSUANT  TO SECTION  13 OR 15(d) OF THE  SECURITIES
     EXCHANGE ACT OF 1934

     For The Transition Period From         to

                         Commission file number 1-3672.

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

            Illinois                                            37-0211380
(State or other jurisdiction of                              (I.R.S. Employer
incorporation or organization)                              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


     Indicate  by check mark  whether the  registrant  (1) has filed all reports
required to be filed by Section 13 or 15(d) of the  Securities  Exchange  Act of
1934  during  the  preceding  12 months  (or for such  shorter  period  that the
registrant was required to file such reports),  and (2) has been subject to such
filing requirements for the past 90 days.


                     Yes          X     .      No               .
                           -------------            ------------


Shares  outstanding of each of registrant's  classes of common stock as of April
 30, 2000:Common Stock, no par value, held by Ameren Corporation (parent company
 of Registrant) - 25,452,373

<PAGE>

                     Central Illinois Public Service Company

                                      Index

                                                                       Page No.

Part I   Financial Information (Unaudited)

         Management's Discussion and Analysis                             2

         Quantitative and Qualitative Disclosure
         About Market Risk                                                5

         Balance Sheet
         - March 31, 2000 and December 31, 1999                           7

         Statement of Income
         - Three months and 12 months ended
            March 31, 2000 and 1999                                       8

         Statement of Cash Flows
         - Three months ended March 31, 2000 and 1999                     9

         Notes to Financial Statements                                   10


Part II  Other Information                                               12

<PAGE>

                    PART I. FINANCIAL INFORMATION (UNAUDITED)

MANAGEMENT'S  DISCUSSION  AND  ANALYSIS OF  FINANCIAL  CONDITION  AND RESULTS OF
OPERATIONS

OVERVIEW

Central  Illinois  Public Service  Company  (AmerenCIPS or the  Registrant) is a
subsidiary of Ameren  Corporation  (Ameren),  a holding company registered under
the Public Utility Holding Company Act of 1935 (PUHCA).  In December 1997, Union
Electric Company  (AmerenUE) and CIPSCO  Incorporated  (CIPSCO) combined to form
Ameren,  with  AmerenUE and CIPSCO's  subsidiaries,  the  Registrant  and CIPSCO
Investment Company (CIC), becoming subsidiaries of Ameren (the Merger).

The following  discussion and analysis  should be read in  conjunction  with the
Notes  to  Financial  Statements  beginning  on page  10,  and the  Management's
Discussion and Analysis of Financial Condition and Results of Operations (MD&A),
the Audited Financial Statements and the Notes to Financial Statements appearing
in the Registrant's 1999 Form 10-K.

RESULTS OF OPERATIONS

Earnings
First  quarter 2000  earnings of $25 million  increased  $12 million from 1999's
first quarter earnings. Earnings for the 12 months ended March 31, 2000 were $62
million, a $16 million decrease from the preceding 12-month period.

Earnings  fluctuated due to many conditions,  primarily:  sales growth,  weather
variations,  electric rate reductions,  gas rate increases,  competitive  market
forces,  fluctuating  operating costs,  changes in interest expense,  changes in
income and  property  taxes and  nonrecurring  charges  for a targeted  employee
separation plan and for coal contract termination payments.

The  significant  items  affecting  revenues,  costs  and  earnings  during  the
three-month  and  12-month  periods  ended March 31, 2000 and 1999 are  detailed
below.

Electric Operations

Electric Operating Revenues      Variations for periods ended March 31, 2000
                                    from comparable prior-year periods
---------------------------------------------------------------------
(Millions of Dollars)              Three Months       Twelve Months
---------------------------------------------------------------------
Rate variations                     $    -              $   (4)
Effect of abnormal weather              (1)                (17)
Growth and other                        15                  23
Interchange sales                       33                 113
---------------------------------------------------------------------
                                    $   47              $  115
---------------------------------------------------------------------


Electric  revenues  for the three months  ended March 31,  2000,  increased  $47
million  compared to the prior  three-  month  period  primarily  driven by a 61
percent increase in interchange sales, due to strong marketing efforts, and a 29
percent increase in native sales. The increase in native sales was primarily due
to  increased  wholesale  and  industrial  sales,   partially  offset  by  lower
residential and commercial sales, due to milder weather.

Electric  revenues  for the 12 months  ended  March  31,  2000,  increased  $115
million,  compared to the same prior year period,  primarily due to increases in
interchange  sales of 39 percent,  due to strong marketing efforts and increases
in native sales of 6 percent.  The increase in native sales was primarily due to
increased  wholesale and  industrial  sales,  partially  offset by reductions in
weather  sensitive  residential and commercial sales of 2 percent and 9 percent,
respectively.  Electric  revenues  were further  reduced by a  residential  rate
decrease.

                                      -2-

<PAGE>



Fuel and Purchased Power             Variations for periods ended March 31, 2000
                                         from comparable prior-year periods
-----------------------------------------------------------------------------
(Millions of Dollars)                    Three Months        Twelve Months
-----------------------------------------------------------------------------
Fuel:
    Generation                             $  11                 $  16
    Price                                     (5)                  (18)
    Generation efficiencies and other          1                    (2)
    Coal contract termination payments         -                    52
Purchased power                               19                    57
-----------------------------------------------------------------------------
                                           $  26                 $ 105
-----------------------------------------------------------------------------


Fuel and  purchased  power  costs  for the three  months  ended  March 31,  2000
increased  $26  million  over the same period in the prior year  primarily  as a
result of increased  generation and purchased  power resulting from higher sales
volume, partially offset by lower fuel prices. The $105 million increase in fuel
and  purchased  power  costs for the 12 months  ended  March 31, 2000 versus the
prior-year period was primarily the result of increased generation and purchased
power resulting from higher sales volume and coal contract termination payments,
partially offset by lower fuel prices.

Gas Operations
Gas revenues for the 12-month  period ended March 31, 2000  increased $5 million
compared to the same year-ago period  primarily due to a gas rate increase which
became  effective in February  1999 and higher gas costs  recovered  through the
Registrant's  purchased gas adjustment  clause.  These  increases were partially
offset  by a 15  percent  decline  in retail  sales,  as well as a  decrease  in
off-system sales to others.

Other Operating Expenses
Other operating expense variations  reflected  recurring factors such as growth,
inflation, labor and benefit increases, in addition to a charge for the targeted
separation plan.

Other operations  expenses increased $3 million for the three months ended March
31,  2000  compared  to the same  year-ago  period  primarily  due to  increased
professional  services,  partially offset by lower employee benefit costs. Other
operations  expenses  increased  $15 million  for the 12 months  ended March 31,
2000,  compared  to  the  same  year-ago  period,  primarily  due  to  increased
postretirement   expenses  resulting  from  changes  in  actuarial  assumptions,
increased  injuries and damages expenses based on claims experience and expenses
associated with deregulation in Illinois.  These increases were partially offset
by a reduced  workforce,  coupled  with the fact that  expenses  for the  twelve
months ended June 30, 1999 included a nonrecurring  pretax charge for a targeted
separation plan of $7 million.

Maintenance  expenses  for the 12 months  ended  March 31,  2000  increased  $28
million  from the  comparable  year-ago  period  due to  increased  power  plant
maintenance.

Taxes
Income taxes for the three  months  ended March 31, 2000,  increased $8 million,
primarily  due to higher  pretax  income.  Income  taxes for the 12 months ended
March 31, 2000, decreased $8 million, primarily due to lower pretax income.

Other  taxes for the 12  months  ended  March 31,  2000,  decreased  $8  million
primarily due to a decrease in gross receipt taxes.  This decrease  results from
the restructuring of the Illinois public utility tax whereby gross receipt taxes
are no longer recorded as electric revenue and gross receipt tax expense.

Other Income and Deductions
For the 12 months ended March 31, 2000,  miscellaneous net increased $3 million,
compared to the same period in the prior  year,  primarily  due to losses on the
disposal of property realized in 1998.

Balance Sheet
Changes in accounts and wages payable,  taxes accrued,  other accounts and notes
receivable,  and other  current  assets  resulted  from the  timing  of  various
payments  to taxing  authorities  and  suppliers.  The $21  million  decrease in

                                      -3-

<PAGE>

intercompany  notes  payable is due to funds  borrowed from a utility money pool
(see Note 5 under Notes to Financial Statements for further information).


LIQUIDITY AND CAPITAL RESOURCES

Cash provided by operating  activities totaled $66 million for the quarter ended
March 31, 2000, compared to $50 million during the same 1999 period.

Cash flows used in investing  activities totaled $20 million and $22 million for
the three  months  ended  March 31,  2000 and 1999,  respectively.  Construction
expenditures  for the three months ended March 31, 2000, for constructing new or
improving existing facilities, were $20 million.

Cash flows used in financing activities totaled $45 million for the three months
ended March 31, 2000,  compared to $38 million during the same 1999 period.  The
Registrant's  principal  financing  activities  for  the  quarter  included  the
redemption of long-term debt and  intercompany  notes payable and the payment of
dividends, partially offset by the issuance of long-term debt. Proceeds from the
issuance  of the  long-term  debt have been set aside in an  environmental  bond
redemption  fund to be used to retire  existing  long-term  indebtedness  in the
second quarter.

The Registrant  plans to continue  utilizing  short-term  debt to support normal
operations and other temporary requirements. The Registrant is authorized by the
Securities  and  Exchange  Commission  under PUHCA to have up to $125 million of
short-term  unsecured debt instruments  outstanding at any one time.  Short-term
borrowings  consist of bank loans  (maturities  generally on an overnight basis)
and commercial  paper  (maturities  generally within 1 to 45 days). At March 31,
2000, the Registrant had committed bank lines of credit  aggregating $30 million
(all of which was  unused and  available  at such  date)  which  make  available
interim  financing  at  various  rates  of  interest  based on  LIBOR,  the bank
certificate of deposit rate or other options.  The lines of credit are renewable
annually at various dates throughout the year. At March 31, 2000, the Registrant
had no outstanding short-term borrowings.

Also, the Registrant has the ability to borrow up to approximately  $950 million
from Ameren or AmerenUE through a regulated money pool agreement.  The regulated
money pool was established to coordinate and provide for certain short-term cash
and working capital requirements and is administered by Ameren Services Company,
another  subsidiary  of Ameren.  Interest  is  calculated  at  varying  rates of
interest  depending on the  composition  of internal  and external  funds in the
regulated  money pool.  At March 31, 2000,  the  Registrant  had $112 million of
intercompany  borrowings  outstanding  and $701  million  available  through the
regulated money pool.

The Registrant,  in the ordinary course of business,  explores  opportunities to
reduce its cost in order to remain  competitive in the marketplace.  Areas where
the Registrant  focuses its review include,  but are not limited to, labor costs
and fuel supply costs. In the labor area, the Registrant has reached  agreements
with all of the Registrant's major collective bargaining units which will permit
it to manage  its labor  costs and  practices  effectively  in the  future.  The
Registrant  also explores  alternatives  to  effectively  manage the size of its
workforce. These alternatives include utilizing hiring freezes,  outsourcing and
offering employee separation  packages.  In the fuel supply area, the Registrant
explores  alternatives  to  effectively  manage its overall  fuel  costs.  These
alternatives include diversifying fuel sources for use at the Registrant's power
plants  (e.g.   utilizing  low-sulfur  versus  high-sulfur  coal),  as  well  as
restructuring or terminating existing contracts with suppliers.

Certain  of  these  cost  reduction  alternatives  could  result  in  additional
investments  being  made at the  Registrant's  power  plants in order to utilize
different  types of coal,  or could  require  nonrecurring  payments of employee
separation  benefits or  nonrecurring  payments to  restructure  or terminate an
existing fuel  contract  with a supplier.  Management is unable to predict which
(if any),  and to what  extent,  these  alternatives  to reduce its overall cost
structure  will be executed.  Management  is unable to  determine  the impact of
these  actions  on  the  Registrant's  future  financial  position,  results  of
operations or liquidity.


ELECTRIC INDUSTRY RESTRUCTURING

In December 1997, the Governor of Illinois signed the Electric  Service Customer
Choice and Rate  Relief Law of 1997 (the Law)  providing  for  electric  utility
restructuring  in Illinois.  This  legislation  introduces  competition into the
supply of electric energy at retail in Illinois.

                                      -4-

<PAGE>

One of the major  provisions of the Law includes the phasing-in  through 2002 of
retail direct access, which allows customers to choose their electric generation
supplier.  The phase-in of retail direct  access began on October 1, 1999,  with
large  commercial and industrial  customers  principally  comprising the initial
group.  The customers in this group  represent  approximately  24 percent of the
Registrant's  total  sales.  As of March 31, 2000,  the impact of retail  direct
access  on  the  Registrant's  financial  condition,  results  of  operation  or
liquidity was immaterial.  Retail direct access will be offered to the remaining
commercial  and  industrial  customers on December 31, 2000,  and to residential
customers on May 1, 2002.

In conjunction with another provision of the Law, on May 1, 2000,  following the
receipt of all required State and Federal regulatory  approvals,  the Registrant
transferred its electric  generating  assets and liabilities,  at historical net
book value, to a newly created  nonregulated  company,  AmerenEnergy  Generating
Company (Generating Company), a subsidiary of AmerenEnergy  Resources Company, a
wholly-owned  subsidiary  of Ameren,  in  exchange  for a  promissory  note from
Generating  Company in the principal  amount of  approximately  $600 million and
Generating  Company common stock.  The promissory  note has a term of five years
and bears interest at 7 percent based on a 10-year amortization. The transferred
assets  represent  a  generating  capacity  of  approximately  2,900  megawatts.
Approximately  45 percent 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,  AmerenEnergy
Marketing  Company  (Marketing  Company),  also  a  wholly-owned  subsidiary  of
AmerenEnergy Resources 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.

The  creation  of the new  subsidiaries  and the  transfer  of the  Registrant's
generating  assets and liabilities had no effect on the financial  statements of
the Registrant as of the date of transfer.


QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

Market risk  represents the risk of changes in value of a financial  instrument,
derivative or non-derivative,  caused by fluctuations in market variables (e.g.,
interest rates, equity prices, commodity prices, etc.). The following discussion
of  Ameren's,   including  AmerenCIPS',   risk  management  activities  includes
"forward-looking"  statements  that  involve  risks  and  uncertainties.  Actual
results could differ  materially from those  projected in the  "forward-looking"
statements. Ameren handles market risks in accordance with established policies,
which may include entering into various derivative  transactions.  In the normal
course of  business,  Ameren also faces risks that are either  non-financial  or
non-quantifiable.  Such risks principally include business,  legal,  operational
and credit risk and are not represented in the following analysis.

Interest Rate Risk
The  Registrant  is exposed to market risk  through  changes in  interest  rates
through its  issuance  of both  long-term  and  short-term  variable-rate  debt,
fixed-rate  debt,  commercial  paper and auction  market  preferred  stock.  The
Registrant manages its interest rate exposure by controlling the amount of these
instruments it holds within its total capitalization portfolio and by monitoring
the effects of market changes in interest rates.

If interest rates increase one percentage point in 2001 as compared to 2000, the
Registrant's  interest  expense would  increase and net income would decrease by
approximately $1 million.  This amount has been determined using the assumptions
that the  Registrant's  outstanding  variable  rate debt,  commercial  paper and
auction market preferred stock as of March 31, 2000, continued to be outstanding
throughout  2001,  and that the  average  interest  rates for these  instruments
increased  one  percentage  point over 2000.  The model  does not  consider  the
effects of the reduced  level of overall  economic  activity that would exist in
such an  environment.  In the event of a significant  change in interest  rates,
management  would likely take  actions to further  mitigate its exposure to this
market risk. However,  due to the uncertainty of the specific actions that would
be taken and their possible effects,  the sensitivity analysis assumes no change
in the Registrant's financial structure.

Commodity Price Risk
The  Registrant  is exposed to changes in market prices for natural gas and fuel
and  electricity.   With  regard  to  its  natural  gas  utility  business,  the
Registrant's  exposure to changing  market prices is in large part  mitigated by
the fact that the  Registrant  has a Purchased  Gas  Adjustment  Clause (PGA) in
place.  The PGA allows the  Registrant to pass on to its customers its prudently
incurred costs of natural gas.

                                      -5-

<PAGE>

Since  the  Registrant  does not  have a  provision  similar  to the PGA for its
electric operations, the Registrant has entered into several long-term contracts
with various  suppliers to purchase  coal to manage its exposure to fuel prices.
With regard to the  Registrant's  exposure to commodity price risk for purchased
power and  excess  electricity  sales,  Ameren  has  established  a  subsidiary,
AmerenEnergy,   Inc.  (AmerenEnergy),   whose  primary  responsibility  includes
managing market risks associated with the changing market prices for electricity
purchased and sold on behalf of the Registrant.

AmerenEnergy  utilizes  several  techniques  to  mitigate  its  market  risk for
electricity,  including utilizing derivative financial instruments. A derivative
is a contract  whose  value is  dependent  on or derived  from the value of some
underlying  asset. The derivative  financial  instruments  that  AmerenEnergy is
allowed to utilize  (which  include  forward  contracts,  futures  contracts and
option  contracts)  are  dictated by a risk  management  policy,  which has been
reviewed with the Auditing Committee of Ameren's Board of Directors.  Compliance
with the risk  management  policy  is the  responsibility  of a risk  management
steering  committee,  consisting  of Ameren  officers  and an  independent  risk
management officer at AmerenEnergy.

As of March 31, 2000, the fair value of derivative financial instruments exposed
to commodity price risk was immaterial.


SAFE HARBOR STATEMENT

Statements made in this Form 10-Q which are not based on historical  facts,  are
"forward-looking"  and, accordingly,  involve risks and uncertainties that could
cause actual results to differ  materially from those  discussed.  Although such
"forward-looking"  statements  have  been  made in good  faith  and are based on
reasonable assumptions,  there is no assurance that the expected results will be
achieved.  These statements include (without limitation) statements as to future
expectations,   beliefs,  plans,  strategies,  objectives,  events,  conditions,
financial  performance  and the Year 2000 Issue.  In  connection  with the "Safe
Harbor" provisions of the Private Securities  Litigation Reform Act of 1995, the
Registrant is providing this cautionary  statement to identify important factors
that could cause actual results to differ materially from those anticipated. The
following factors,  in addition to those discussed  elsewhere in this report and
in the Annual  Report on Form 10-K for the fiscal year ended  December 31, 1999,
and in subsequent  securities filings,  could cause results to differ materially
from management expectations as suggested by such "forward-looking"  statements:
the  effects  of  regulatory  actions;  changes  in laws and other  governmental
actions;  the impact on the  Registrant  of current  regulations  related to the
phasing-in of the  opportunity for some customers to choose  alternative  energy
suppliers in Illinois;  the effects of increased  competition  in the future due
to, among other  things,  deregulation  of certain  aspects of the  Registrant's
business at both the State and Federal levels; future market prices for fuel and
purchased power,  electricity,  and natural gas,  including the use of financial
instruments; average rates for electricity in the Midwest; business and economic
conditions;  interest rates;  weather conditions;  fuel prices and availability;
generation plant performance; the impact of current environmental regulations on
utilities and  generating  companies  and the  expectation  that more  stringent
requirements  will be  introduced  over time,  which  could  potentially  have a
negative  financial  effect;  monetary  and fiscal  policies;  future  wages and
employee benefits costs; and legal and administrative proceedings.

                                      -6-

<PAGE>

<TABLE>
<CAPTION>

                     CENTRAL ILLINOIS PUBLIC SERVICE COMPANY
                                  BALANCE SHEET
                                    UNAUDITED
                                    ---------
                      (Thousands of Dollars, Except Shares)


                                                                 March 31,  December 31,
ASSETS                                                             2000         1999
------                                                          ----------   ----------
Property and plant, at original cost:
<S>                                                            <C>          <C>
   Electric                                                     $2,460,012   $2,422,002
   Gas                                                             270,029      267,909
                                                                ----------   ----------
                                                                 2,730,041    2,689,911
   Less accumulated depreciation and amortization                1,271,760    1,260,582
                                                                ----------   ----------
                                                                 1,458,281    1,429,329
Construction work in progress                                       12,184       43,435
                                                                ----------   ----------
         Total property and plant, net                           1,470,465    1,472,764
                                                                ----------   ----------

Other assets                                                        17,831       17,722

Current assets:
   Cash and cash equivalents                                        13,176       12,536
   Environmental bond redemption fund                               51,100         --
   Accounts receivable - trade (less allowance for doubtful
         accounts of $2,184 and $1,828, respectively)               64,214       48,703
   Unbilled revenue                                                 55,279       75,884
   Other accounts and notes receivable                              20,363       20,875

   Materials and supplies, at average cost -
      Fossil fuel                                                   39,084       47,291
      Other                                                         29,319       33,931
   Other                                                             9,787       10,387
                                                                ----------   ----------
         Total current assets                                      282,322      249,607
                                                                ----------   ----------
Regulatory assets:
   Deferred income taxes                                            21,520       21,520
   Other                                                             8,264       20,141
                                                                ----------   ----------
         Total regulatory assets                                    29,784       41,661
                                                                ----------   ----------
Total Assets                                                    $1,800,402   $1,781,754
                                                                ==========   ==========

CAPITAL AND LIABILITIES
Capitalization:
   Common stock, no par value, 45,000,000 shares authorized -
     25,452,373 shares outstanding                              $  120,033   $  120,033
   Retained earnings                                               421,594      414,345
                                                                ----------   ----------
         Total common stockholder's equity                         541,627      534,378
   Preferred stock not subject to mandatory redemption              80,000       80,000
   Long-term debt                                                  488,086      493,625
                                                                ----------   ----------
        Total capitalization                                     1,109,713    1,108,003
                                                                ----------   ----------
Current liabilities:
   Current maturity of long-term debt                               87,000       35,000
   Intercompany notes payable                                      111,720      132,900
   Accounts and wages payable                                       61,143       82,800
   Accumulated deferred income taxes                                22,621       22,621
   Taxes accrued                                                    51,003       32,145
   Other                                                            41,279       39,619
                                                                ----------   ----------
         Total current liabilities                                 374,766      345,085
                                                                ----------   ----------
Accumulated deferred income taxes                                  210,078      216,661
Accumulated deferred investment tax credits                         33,368       32,169
Regulatory liability                                                36,981       34,004
Other deferred credits and liabilities                              35,496       45,832
                                                                ----------   ----------
Total Capital and Liabilities                                   $1,800,402   $1,781,754
                                                                ==========   ==========

</TABLE>

See Notes to Financial Statements.

                                      -7-

<PAGE>

<TABLE>
<CAPTION>

                     CENTRAL ILLINOIS PUBLIC SERVICE COMPANY
                               STATEMENT OF INCOME
                                    UNAUDITED
                                    ---------
                             (Thousands of Dollars)


                                                  Three Months Ended     Twelve Months Ended
                                                      March 31,               March 31,
                                                 -------------------     --------------------
                                                  2000        1999         2000         1999
                                                  ----        ----         ----         ----

 OPERATING REVENUES:
<S>                                          <C>          <C>          <C>          <C>
    Electric                                  $ 202,503    $ 155,240    $ 842,739    $ 727,887
    Gas                                          52,824       52,532      132,938      127,794
                                              ---------    ---------    ---------    ---------
 Total operating revenues                       255,327      207,772      975,677      855,681

 OPERATING EXPENSES:
    Operations
       Fuel and purchased power                  81,630       55,690      340,148      234,693
       Gas                                       31,714       33,250       71,816       70,375
       Other                                     42,996       40,398      193,220      178,581
                                              ---------    ---------    ---------    ---------
                                                156,340      129,338      605,184      483,649
    Maintenance                                  16,504       17,407      102,679       75,114
    Depreciation and amortization                21,350       20,740       81,167       76,241
    Income taxes                                 14,163        5,979       38,957       47,400
    Other taxes                                  11,236        9,599       41,950       50,256
                                              ---------    ---------    ---------    ---------
       Total operating expenses                 219,593      183,063      869,937      732,660

 OPERATING INCOME                                35,734       24,709      105,740      123,021

 OTHER INCOME AND (DEDUCTIONS):
    Allowance for equity funds used
       during construction                         --             (6)          (2)         (36)
    Miscellaneous, net                              377          356        2,051         (953)
                                              ---------    ---------    ---------    ---------
        Total other income and (deductions)         377          350        2,049         (989)

 INCOME BEFORE
    INTEREST CHARGES                             36,111       25,059      107,789      122,032

 INTEREST CHARGES:
    Interest                                      9,559       10,815       41,480       40,422
    Allowance for borrowed funds
       used during construction                     220          (71)         312         (734)
                                              ---------    ---------    ---------    ---------
    Net interest charges                          9,779       10,744       41,792       39,688
                                              ---------    ---------    ---------    ---------

NET INCOME                                       26,332       14,315       65,997       82,344

PREFERRED STOCK DIVIDENDS                           993          968        3,858        3,729
                                              ---------    ---------    ---------    ---------
NET INCOME AFTER PREFERRED
   STOCK DIVIDENDS                            $  25,339    $  13,347    $  62,139    $  78,615
                                              =========    =========    =========    =========

</TABLE>

See Notes to Financial Statements.

                                      -8-

<PAGE>

<TABLE>
<CAPTION>

                     CENTRAL ILLINOIS PUBLIC SERVICE COMPANY
                             STATEMENT OF CASH FLOWS
                                    UNAUDITED
                                    ---------
                             (Thousands of Dollars)




                                                          Three Months Ended
                                                              March 31,
                                                          ------------------
                                                          2000        1999
                                                          ----        ----
Cash Flows From Operating:
<S>                                                   <C>         <C>
   Net income                                          $ 26,332    $ 14,315
   Adjustments to reconcile net income to net cash
      provided by operating activities:
        Depreciation and amortization                    21,350      20,740
        Allowance for funds used during construction        220         (65)
        Deferred income taxes, net                       (1,792)     (4,975)
        Deferred investment tax credits, net              1,199        (621)
        Changes in assets and liabilities:
           Receivables, net                               5,606      (5,278)
           Materials and supplies                        12,819       8,657
           Accounts and wages payable                   (21,657)     (4,690)
           Taxes accrued                                 18,858       9,641
           Other, net                                     2,797      12,187
                                                       --------    --------
Net cash provided by operating activities                65,732      49,911

Cash Flows From Investing:
   Construction expenditures                            (19,642)    (22,075)
   Allowance for funds used during construction            (220)         65
                                                       --------    --------
Net cash used in investing activities                   (19,862)    (22,010)

Cash Flows From Financing:
   Dividends on common stock                            (18,057)    (17,155)
   Dividends on preferred stock                            (993)       (926)
   Environmental bond redemption fund                   (51,100)       --
   Redemptions -
      Short-term debt                                      --       (15,000)
      Long-term debt                                     (5,000)     (5,000)
      Intercompany notes payable                        (21,180)       --
   Issuances -
      Long-term debt                                     51,100        --
                                                       --------    --------
Net cash used in financing activities                   (45,230)    (38,081)
                                                       --------    --------

Net change in cash and cash equivalents                     640     (10,180)
Cash and cash equivalents at beginning of year           12,536      10,180
                                                       --------    --------
Cash and cash equivalents at end of period             $ 13,176    $   --
                                                       ========    ========

Cash paid during the periods:
   Interest (net of amount capitalized)                $  9,678    $  8,750
   Income taxes, net                                   $   --      $    754

</TABLE>

See Notes to Financial Statements.

                                      -9-

<PAGE>

CENTRAL ILLINOIS PUBLIC SERVICE COMPANY
NOTES TO FINANCIAL STATEMENTS (UNAUDITED)
March 31, 2000


Note 1 - Central Illinois Public Service Company  (AmerenCIPS or the Registrant)
is a subsidiary of Ameren Corporation  (Ameren),  which is the parent company of
two utility  operating  companies,  the Registrant  and Union  Electric  Company
(AmerenUE).  Ameren is a registered  holding  company  under the Public  Utility
Holding  Company Act of 1935 (PUHCA)  formed in December 1997 upon the merger of
CIPSCO  Incorporated (the Registrant's former parent) and AmerenUE (the Merger).
Both Ameren and its subsidiaries are subject to the regulatory provisions of the
PUHCA.  The  operating  companies  are engaged  principally  in the  generation,
transmission,  distribution  and  sale of  electric  energy  and  the  purchase,
distribution,  transportation  and sale of natural gas in the states of Illinois
and  Missouri.  Contracts  among the  companies--dealing  with  jointly-operated
generating facilities,  interconnecting  transmission lines, and the exchange of
electric power--are regulated by the Federal Energy Regulatory Commission (FERC)
or the Securities and Exchange Commission (SEC). Administrative support services
are provided to the Registrant by a separate Ameren subsidiary,  Ameren Services
Company.  The Registrant  serves 400,000 electric and 175,000 gas customers in a
20,000 square-mile region of central and southern Illinois.

In  conjunction  with the Illinois  Electric  Service  Customer  Choice and Rate
Relief  Law of 1997 (the  Law),  on May 1, 2000,  following  the  receipt of all
required State and Federal regulatory approvals,  the Registrant transferred its
electric  generating assets and liabilities,  at historical net book value, to a
newly created nonregulated company,  AmerenEnergy Generating Company (Generating
Company),  a  subsidiary  of  AmerenEnergy  Resources  Company,  a  wholly-owned
subsidiary of Ameren, in exchange for a promissory note from Generating  Company
in the principal  amount of  approximately  $600 million and Generating  Company
common stock. The promissory note has a term of five years and bears interest at
7 percent based on a 10-year  amortization.  The transferred  assets represent a
generating capacity of approximately  2,900 megawatts.  Approximately 45 percent
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,  AmerenEnergy
Marketing  Company  (Marketing  Company),  also  a  wholly-owned  subsidiary  of
AmerenEnergy Resources 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.

The Registrant also has a 20 percent  interest in Electric  Energy,  Inc. (EEI),
which is  accounted  for under the  equity  method of  accounting.  EEI owns and
operates an  electric  generating  and  transmission  facility in Illinois  that
supplies  electric  power  primarily to a uranium  enrichment  plant  located in
Paducah, Kentucky.

Note 2 - Financial  statement note  disclosures,  normally included in financial
statements prepared in conformity with generally accepted accounting principles,
have been omitted in this Form 10-Q pursuant to the Rules and Regulations of the
SEC.  However,  in the opinion of the Registrant,  the disclosures  contained in
this Form 10-Q are adequate to make the  information  presented not  misleading.
See Notes to Financial Statements included in the 1999 Form 10-K for information
relevant to the  financial  statements  contained  in this Form 10-Q,  including
information as to the significant accounting policies of the Registrant.

Note 3 - In the  opinion of the  Registrant,  the interim  financial  statements
filed as part of this Form 10-Q  reflect  all  adjustments,  consisting  only of
normal recurring adjustments,  necessary for a fair statement of the results for
the periods presented.  The Registrant's  financial  statements were prepared to
permit the information  required in the Financial Data Schedule  (FDS),  Exhibit
27,  to be  directly  extracted  from  the  filed  statements.  The FDS  amounts
correspond  to or are  calculable  from the amounts  reported  in the  financial
statements or notes thereto.

Note 4 - Due to the  effect of  weather  on sales and  other  factors  which are
characteristic of public utility  operations,  financial results for the periods
ended March 31, 2000 and 1999, are not necessarily  indicative of trends for any
three-month or 12-month period.

Note 5 - The Registrant has  transactions  in the normal course of business with
other Ameren  subsidiaries.  These transactions are primarily comprised of power
purchases and sales and services received or rendered.  Intercompany receivables
included in other accounts and notes receivable were  approximately  $15 million
and $12  million,

                                      -10-

<PAGE>

respectively,  as of March 31, 2000 and December 31, 1999. Intercompany payables
included  in  accounts  and  wages  payable  totaled  approximately  $17 and $35
million, respectively, as of March 31, 2000 and December 31, 1999.

In addition,  the Registrant has the ability to borrow up to approximately  $950
million from Ameren or AmerenUE or invest funds  through a regulated  money pool
agreement.  The regulated  money pool was  established to coordinate and provide
for certain short-term cash and working capital requirements and is administered
by Ameren Services Company.  Interest is calculated at varying rates of interest
depending on the  composition  of internal and external  funds in the  regulated
money pool. At March 31, 2000, the  Registrant had $112 million of  intercompany
borrowings  outstanding  and $701million  available  through the regulated money
pool.

Note 6 - Segment  information  for the three  month and 12 month  periods  ended
March 31, 2000 and 1999 is as follows:

<TABLE>
<CAPTION>

--------------------------------------------------------------------------------

(in thousands)                             Electric       Gas           Total
--------------------------------------------------------------------------------

Three months ended March 31, 2000:

<S>                                     <C>            <C>           <C>
Revenues                                 $202,503       $52,824       $255,327
Operating Income                           30,032         5,702         35,734
--------------------------------------------------------------------------------

Three months ended March 31, 1999:

Revenues                                 $155,240       $52,532       $207,772
Operating Income (Loss)                    19,816         4,893         24,709
--------------------------------------------------------------------------------

12 months ended March 31, 2000:

Revenues                                 $842,739       $132,938      $975,677
Operating Income                           95,903          9,837       105,740
--------------------------------------------------------------------------------

12 months ended March 31, 1999:

Revenues                                 $727,887       $127,794      $855,681
Operating Income                          115,795          7,226       123,021
--------------------------------------------------------------------------------

</TABLE>

                                      -11-

<PAGE>



                           PART II. OTHER INFORMATION


ITEM 1. LEGAL PROCEEDINGS
        -----------------

     Reference  is  made  to  "Liquidity  and  Capital   Resources"  in  Item 7.
Management's  Discussion  and  Analysis of  Financial  Condition  and Results of
Operations and Note 11 - Commitments and Contingencies in the Notes to Financial
Statements in the  Registrant's  Form 10-K for the year ended December 31, 1999,
for information  regarding the United States  Environmental  Protection Agency's
(EPA) issuance in 1997 of National  Ambient Air Quality  Standards for ozone and
particulate  matter.  In May 1999,  the United  States  Court of Appeals for the
District  of  Columbia   Circuit  remanded  the  ambient  air  quality  standard
regulations  to the EPA for  reconsideration.  In January and February 2000, the
parties to the  litigation  filed  petitions for review before the United States
Supreme Court.  The Supreme Court has not decided whether to accept the case for
review. At this time, the Registrant is unable to predict the ultimate impact of
those revised air quality standards on its future financial  condition,  results
of operations or liquidity.


ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS
        ---------------------------------------------------

     At the annual meeting of  stockholders  of the Registrant held on April 25,
2000,  the  following  matter was  presented  to the  meeting for a vote and the
results of such voting are as follows:

     Item (1) Election of Directors.

                                                                       Non-Voted
                   Name                  For            Withheld        Brokers
                   ----                  ---            --------        -------

     Paul A. Agathen..............    25,940,091         5,854             0
     Warner L. Baxter.............    25,940,226         5,749             0
     Donald E. Brandt.............    25,940,231         5,744             0
     Charles W. Mueller...........    25,940,241         5,734             0
     Gary L. Rainwater............    25,940,236         5,739             0


ITEM 6. EXHIBITS AND REPORTS ON FORM 8-K
        --------------------------------

     (a)  Exhibits.

          Exhibit 12 -  Computation  of Ratio of Earnings  to Fixed  Charges and
          Preferred Stock Dividend Requirements, 12 Months Ended March 31, 2000.

          Exhibit 27 - Financial Data Schedule.

          The  following  instrument  defining  the rights of holders of certain
          unregistered  long-term debt of AmerenCIPS has not been filed with the
          Securities and Exchange Commission but will be furnished upon request.

          1.   Loan  Agreement  dated  March 1,  2000,  between  AmerenCIPS  and
               Illinois  Development Finance Authority (IDFA) in connection with
               the IDFA's $51,100,000  Pollution Control Revenue Refunding Bonds
               (AmerenCIPS Project) Series 2000A due March 1, 2014.

     (b)  Reports on Form 8-K. None.

                                      -12-

<PAGE>

                                   SIGNATURES

     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 15, 2000

                                      -13-