FORM 11-K




                   (X) ANNUAL REPORT PURSUANT TO SECTION 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

                   FOR THE FISCAL YEAR ENDED DECEMBER 31, 2001

                                       OR

                 ( ) TRANSITION REPORT PURSUANT TO SECTION 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934
                    For the transition period from       to
                                                  ------   -----

                         COMMISSION FILE NUMBER 1-14756









                               AMEREN CORPORATION
                             SAVINGS INVESTMENT PLAN





                           Issuer: Ameren Corporation


                              1901 Chouteau Avenue
                            St. Louis, Missouri 63103
                          (Principal Executive Office)



Ameren Corporation
Savings Investment Plan
Report, Financial Statements and Additional Information
December 31, 2001 and 2000



Ameren Corporation
Savings Investment Plan

Index to Report, Financial Statements
and Additional Information
December 31, 2001 and 2000
--------------------------------------------------------------------------------

                                                                      Page

Report of Independent Accountants                                      1

Statement of Net Assets Available for
 Benefits at December 31, 2001 and 2000                                2

Statement of Changes in Net Assets Available
 for Benefits for the years ended December 31, 2001 and 2000           3

Notes to Financial Statements                                         4-11

Additional Information*:
     Schedule of Assets (Held at End of Year)
      December 31, 2001                                             Schedule I








*    Other schedules required by 29 CFR 2520.103-10 of the Department of Labor's
     Rules and  Regulations  for Reporting and Disclosure  under ERISA have been
     omitted because they are not applicable.





              Report of Independent Accountants

To the Participants and Administrator of
the Ameren Corporation
Savings Investment Plan


In our opinion, the accompanying  statement of net assets available for benefits
and the  related  statement  of  changes in net assets  available  for  benefits
present fairly, in all material respects,  the net assets available for benefits
of the Ameren  Corporation  Savings Investment Plan (the "Plan") at December 31,
2001 and 2000,  and the changes in net assets  available  for  benefits  for the
years then ended in conformity with accounting  principles generally accepted in
the United States of America.  These financial statements are the responsibility
of the Plan's  management;  our responsibility is to express an opinion on these
financial  statements  based on our  audits.  We  conducted  our audits of these
statements  in  accordance  with auditing  standards  generally  accepted in the
United  States of America,  which  require that we plan and perform the audit to
obtain reasonable  assurance about whether the financial  statements are free of
material  misstatement.  An audit includes examining,  on a test basis, evidence
supporting the amounts and  disclosures in the financial  statements,  assessing
the accounting principles used and significant estimates made by management, and
evaluating the overall  financial  statement  presentation.  We believe that our
audits provide a reasonable basis for our opinion.

Our audits  were  conducted  for the  purpose of forming an opinion on the basic
financial statements taken as a whole. The supplemental schedule of assets (held
at end of year) is presented for the purpose of additional analysis and is not a
required part of the basic financial statements but is supplementary information
required by the  Department of Labor's Rules and  Regulations  for Reporting and
Disclosure  under the Employee  Retirement  Income  Security  Act of 1974.  This
supplemental  schedule  is the  responsibility  of the  Plan's  management.  The
supplemental  schedule has been subjected to the auditing  procedures applied in
the audits of the basic  financial  statements  and, in our  opinion,  is fairly
stated in all material  respects in relation to the basic  financial  statements
taken as a whole.



/s/ PricewaterhouseCoopers LLP
PricewaterhouseCoopers LLP
St. Louis, Missouri
June 27, 2002





Ameren Corporation
Savings Investment Plan

Statement of Net Assets Available for Benefits
December 31, 2001 and 2000
--------------------------------------------------------------------------------
                                                             December 31,

                                                      2001               2000

Investments (see Note 3)                           $683,613,115     $683,128,881

Cash                                                    388,626             --

Receivables:
    Participant contributions                         1,353,420        1,152,583
    Employer contributions                              568,020          469,767
    Dividends and interest                               35,356          376,108
    Due from broker for securities sold               1,014,395             --
                                                   ------------     ------------
Net assets available for benefits                  $686,972,932     $685,127,339
                                                   ============     ============



   The accompanying notes are an integral part of these financial statements.


                                      -2-



Ameren Corporation
Savings Investment Plan

Statement of Changes in Net Assets Available for Benefits
For the Years Ended December 31, 2001 and 2000
--------------------------------------------------------------------------------

                                                For the year ended December 31,
                                                      2001             2000

Investment (loss) income:
    Interest and dividends                      $  15,069,266    $  16,375,021
    Net (depreciation) appreciation
     in fair value of investments                 (49,526,185)      48,893,251
                                                --------------   -------------
                                                  (34,456,919)      65,268,272
                                                --------------   -------------

Participant contributions                          39,907,028       33,399,018
Employer contributions                             12,511,947       11,076,019
                                                -------------    -------------
                                                   52,418,975       44,475,037
                                                -------------    -------------

Plan transfer in (see Note 7)                      20,211,328             --
                                                -------------    -------------

Benefits paid to participants                      36,247,614       49,542,280
Administrative expenses                                80,177           75,128
                                                -------------    -------------
                                                   36,327,791       49,617,408
                                                -------------    -------------

Net increase                                        1,845,593       60,125,901

Net assets available for benefits:
  Beginning of year                               685,127,339      625,001,438
                                                -------------    -------------
  End of year                                   $ 686,972,932    $ 685,127,339
                                                =============    =============




   The accompanying notes are an integral part of these financial statements.


                                      -3-


Ameren Corporation
Savings Investment Plan

Notes to Financial Statements
December 31, 2001 and 2000
--------------------------------------------------------------------------------

1.   Description of the Plan

     General
     The  following is a brief  summary of the various  provisions of the Ameren
     Corporation (the Company) Savings Investment Plan (the Plan).  Participants
     should refer to the Plan document for more complete information.

     The Plan's purpose is to provide certain  management and contract employees
     of the  Company  and its  wholly-owned  subsidiaries  the option to defer a
     portion of their annual base  compensation  for Federal income tax purposes
     in accordance with Section 401(k) of the Internal Revenue Code. The Plan is
     subject to certain  provisions of the Employee  Retirement  Income Security
     Act of 1974 (ERISA),  as amended,  and  regulations  of the  Securities and
     Exchange Commission.

     The  Company  serves as sponsor  of the Plan,  and,  consequently,  has the
     authority to amend or terminate  the Plan subject to certain  restrictions.
     The Board of Directors of the Company has the authority and  responsibility
     for the general  administration of the Plan. The Northern Trust Company, as
     Trustee,  has the  authority  and  responsibility  to hold and  protect the
     assets of the Plan in  accordance  with Plan  provisions  and the  separate
     Trust Agreement.

     Effective January 1, 2001, the Ameren Corporation  Employee Stock Ownership
     Plan for Certain Employees of CIPS, which was a plan that provided eligible
     Company  employees with ownership  shares of Company stock, was merged with
     the Plan (see Note 7).

     Effective  December  2001,  when  dividends  are paid on shares of  Company
     common stock held in the Ameren Stock Fund, these dividends  purchase newly
     issued  shares of Company  common stock  instead of being  purchased in the
     open market.

     Participation
     The Plan covers  substantially all employees of the Company except contract
     employees covered by a collective  bargaining  agreement between AmerenCIPS
     Local 702 IBEW or AmerenCIPS Local 148 IUOE and the Company. Effective July
     1, 2001, the Plan was amended to allow  AmerenCIPS  Local 148 (Clerical) to
     participate  in the Plan.  All regular full time  employees are eligible to
     participate  upon  employment.   Participation  by  eligible  employees  is
     voluntary.

     Contributions  Participants  may contribute from 1% up to 15% of their base
     compensation  to the Plan  through  payroll  deductions.  Company  matching
     contributions for contract employees are made based on specific  agreements
     between the Company and the individual  collective  bargaining  units.  For
     management  employees,  the Company makes a matching  contribution  ranging
     from $.25 to $.75 for each  $1.00 up to the first 6% of each  participant's
     contribution (basic matching  contribution).  In addition, the Company will
     contribute   $.25  for  each  $1.00  for  the  next  3%  of  a   management
     participant's contribution (additional matching contribution). For contract
     employees,  the Company makes a matching  contribution ranging from $.15 to
     $.75 for each $1.00 up to the first 6% of each  participant's  contribution
     (basic matching contribution). In addition,

                                      -4-

Ameren Corporation
Savings Investment Plan

Notes to Financial Statements
December 31, 2001 and 2000
--------------------------------------------------------------------------------

     the  Company  will  contribute  $.10 to $.25 for  each  $1.00 up to 3% of a
     participant's contribution (additional matching contribution). A portion of
     Company matching contributions is invested in the Ameren Common Stock Fund.
     All Company  contributions are made to the extent  sufficient  earnings are
     available.

     Participants  direct  their basic  contributions  and the  Company's  basic
     matching  contributions by electing that such  contributions be placed in a
     single  investment fund or allocated in increments of 1% to any combination
     of investment funds.  Such fund allocation  elections may be changed daily.
     Earnings  derived from the assets of any investment  fund are reinvested in
     the fund to which they relate.  Participants  may elect daily to reallocate
     all or in 1% increments, the value of their accounts between funds. Pending
     investment  of the  assets  into  any  investment  fund,  the  Trustee  may
     temporarily make certain short-term investments.

     Participant Loans
     The Plan  permits  participants  to borrow from their  accounts  within the
     Plan. Such borrowings may be made subject to the following: (1) the minimum
     amount of the loan is $1,000, (2) the amount of the loan may not exceed the
     lesser  of  $50,000  or  fifty   percent  of  the  vested   amount  in  the
     participant's  account,  (3) the loan will bear a fixed  interest  rate and
     repayments  will  be made  through  mutual  agreement  subject  to  certain
     statutory  repayment time limits, (4) the fixed interest rate will be equal
     to the  "corporate  base rate of interest" as announced by the Trustee plus
     1%,  and (5) such  other  rules and  regulations  as may be  adopted by the
     Company.  At December 31, 2001 and 2000,  the interest rates on participant
     loans ranged from 7% to 10.5%.

     Vesting
     The amounts in participants' accounts, including Company contributions, are
     fully vested at all times.

     Payment of Benefits
     The total amount of a  participant's  account shall be  distributed  to the
     participant  according  to one of the  options  as  described  in the  Plan
     document and as elected by the  participant.  A  participant  whose account
     balance is $5,000 or greater may defer  distribution  until  December 31 of
     the year they  attain  age  70-1/2  but no later  than  April 1 of the year
     following the  participant's  attaining  age 70-1/2.  If the balance of the
     account is less than $5,000,  the distribution  shall be made no later than
     120 days after close of the plan year.  All  distributions  shall be in the
     form of cash.  Participants  may elect to have his or her  interest  in the
     Ameren Stock Fund, if  applicable,  distributed  in shares of Ameren common
     stock.  Participants may withdraw certain basic  contributions  and related
     earnings thereon upon reaching age 59-1/2, in the event of total disability
     or financial  hardship as defined by the Plan or the Code.  For purposes of
     distributions, the participant's account value will be determined as of the
     last  business day  coincident  with or  immediately  preceding  the day of
     distribution.  Contributions to the Plan and investment  income thereon are
     taxable to participants  upon  distribution  pursuant to the rules provided
     for under the Plan and the Internal Revenue Code.

                                      -5-

Ameren Corporation
Savings Investment Plan

Notes to Financial Statements
December 31, 2001 and 2000
--------------------------------------------------------------------------------

     The Plan also  provides,  to  participants  of the  former  Union  Electric
     Company  Employee Stock  Ownership  Plan and the former Ameren  Corporation
     Employee  Stock  Ownership  Plan for Certain  Employees  of CIPS and at the
     discretion  of the  Company,  for  distribution  prior  to  termination  of
     employment  of (a) all or a  portion  of a  participant's  account  balance
     acquired at least 84 months prior to a distribution  and (b) any portion of
     a participant's account balance acquired by dividends or other income.

     Plan Termination
     The Company intends to continue the Plan indefinitely. However, the Company
     may at any time and for any reason,  subject to ERISA and Internal  Revenue
     Service  regulations,  suspend or  terminate  the Plan  provided  that such
     action  does  not   retroactively   adversely  affect  the  rights  of  any
     participant under the Plan.

2.   Summary of Significant Accounting Policies

     Basis of Accounting
     The  accompanying  financial  statements  of the Plan are  prepared  on the
     accrual basis of accounting.

     Use of Estimates
     The  preparation  of financial  statements  in conformity  with  accounting
     principles  generally  accepted  in the United  States of America  requires
     management  to make  estimates  and  assumptions  that affect the  reported
     amounts of assets and liabilities  and disclosure of contingent  assets and
     liabilities  at the  date of the  financial  statements  and  the  reported
     amounts  of  changes in net assets  during  the  reporting  period.  Actual
     results could differ from those estimates.

     Investments
     All  investments  are  presented  at fair value as of December 31, 2001 and
     2000. The fair value of the Ameren Common Stock Fund was  determined  using
     year-end  published  market prices.  Investments  in equity  securities and
     bonds are valued at net asset market value including  accrued income on the
     last business day of each year. Investments in the Northern Trust Company's
     Short-term  Fund and the T. Rowe Price  Stable  Value Common Trust Fund are
     valued at cost plus accrued income, which approximates market.  Participant
     loans are valued at cost which approximates fair market value.

     Investment  securities are exposed to various risks, such as interest rate,
     market,  and  credit.  Due to the  level of risk  associated  with  certain
     investment  securities and the level of  uncertainty  related to changes in
     the value of investment securities, it is at least reasonably possible that
     changes  in risks in the near term  could  materially  affect  the  amounts
     reported in the Statement of Net Assets Available for Benefits.

                                      -6-

Ameren Corporation
Savings Investment Plan

Notes to Financial Statements
December 31, 2001 and 2000
--------------------------------------------------------------------------------

     Income
     Interest  income is  recorded  on the  accrual  basis.  Dividend  income is
     recorded on the ex-dividend date.

     Gains and losses on security  transactions  are recorded on the trade date.
     Net unrealized  appreciation or  depreciation  for the year is reflected in
     net  appreciation  (depreciation)  in  fair  value  of  investments  on the
     Statement of Changes in Net Assets Available for Benefits.

     Expenses
     Trustee fees incurred in administering the Plan are charged to the Plan.

     Benefit Payments
     Benefit payments are recorded when paid.


                                      -7-

Ameren Corporation
Savings Investment Plan

Notes to Financial Statements
December 31, 2001 and 2000
--------------------------------------------------------------------------------

3.   Investments

     The following table presents investments of the Plan.


                                                             December 31
                                                        2001            2000
Investments at Fair Value as Determined
By Quoted Market Price
                                                                
Common Stock:
    Ameren Corporation, $.01 par value         $180,505,606   $169,135,704

Managed Equity Funds:
    MSIF Trust Fund                                 124,134,320    126,066,390
    Barclays Global Investors Equity Index Fund     46,661,437      54,263,419
    Vanguard US Growth Fund                         39,883,621      59,519,864
    Washington Mutual Investors Fund                87,789,899      80,059,794
Vanguard Asset Allocation Fund
    Vanguard Asset Allocation Fund                  68,541,101      75,163,540
    Vanguard Extended Market Index Fund                  5,349,502           --

Managed International Equity Fund:
    American Funds Group Europacific Growth Fund        21,609,653      27,460,114

Investments at Estimated Fair Value

T. Rowe Price Stable Value Common Trust Fund        85,156,018      70,965,971

MFO Pimco Funds                                          4,522,490           --

Northern Trust Company's Short-Term Investment Fund      3,184,174       4,436,206

Participant Loans                                       16,275,294      16,057,879
                                                      ------------    ------------

                                                      $683,613,115    $683,128,881
                                                      ============    ============



 Investments that represent 5 percent or more of the Plan's net assets.
 Non-participant directed portion is $36,441,059, and $33,571,135 at
     December 31, 2001 and 2000, respectively.

                                      -8-


Ameren Corporation
Savings Investment Plan

Notes to Financial Statements
December 31, 2001 and 2000
--------------------------------------------------------------------------------

During 2001 and 2000,  the Plan's  investments  (including  investments  bought,
sold, and held during the year) appreciated (depreciated) in value as follows:


                                                     Year Ended December 31,
                                                     2001              2000

Investments at Fair Value as Determined
By Market Price

Managed Fund Investments                          $(33,661,710)   $ (5,038,617)
Ameren Corporation Common Stock                    (15,856,027)     53,929,195
                                                  -------------    -------------
Net change in fair value                           (49,517,737)     48,890,578

Investments at Estimated Fair Value

Short-term Investments                                  (8,448)          2,673
                                                  -------------   -------------
Net change in fair value                          $(49,526,185)   $ 48,893,251
                                                  =============   =============

4.   Nonparticipant-Directed Investments

     Information  about the net assets  and the  significant  components  of the
     changes in net assets relating to the  nonparticipant-directed  investments
     is as follows:

                                                            December 31,
                                                      2001             2000

Net assets:
    Ameren Corporation common stock               $ 36,441,059    $ 33,571,135
    Employer contributions receivable                  332,379         274,908

Changes in net assets:
    Dividends                                        1,985,449       1,671,933
    Net (depreciation) appreciation in fair
     value of investments                           (2,731,877)      9,242,845
    Employer contributions                           4,426,367       4,023,598
    Benefits paid to participants                      583,065         856,152



5.   Transactions with Parties-in-Interest

     At December  31, 2001,  the Plan held Company  common stock with a cost and
     market value of $135,847,679 and $180,505,606,  respectively.  During 2001,
     the Plan purchased  shares at a cost of $17,671,216  and sold shares valued
     at  $6,327,522,  resulting in a net realized gain of  $1,824,049.  The Plan
     also  distributed  shares valued at $3,243,979 to persons  withdrawing from
     the Plan.


                                      -9-

Ameren Corporation
Savings Investment Plan

Notes to Financial Statements
December 31, 2001 and 2000
--------------------------------------------------------------------------------

     At December  31, 2000,  the Plan held Company  common stock with a cost and
     market value of $112,233,148 and $169,135,704,  respectively.  During 2000,
     the Plan purchased  shares at a cost of $16,685,329  and sold shares valued
     at  $29,781,870,  resulting in a net realized gain of $6,318,759.  The Plan
     also  distributed  shares valued at $4,174,577 to persons  withdrawing from
     the Plan.

     The Plan  held  $3,184,174  and  $4,436,206  in  Northern  Trust  Company's
     Collective  Short-term  Investment  Fund at  December  31,  2001 and  2000,
     respectively.

     These  transactions  are  allowable  party-in-interest  transactions  under
     Section 408(b)(8) of the ERISA regulations.

6.   Reconciliation of Financial Statements to Form 5500

     The following is a reconciliation  of net assets available for benefits per
     the financial statements to the Form 5500:

                                                           December 31,
                                                      2001             2000

Net assets available for benefits per the
 financial statements                            $ 686,972,932    $ 685,127,339
Amounts allocated to withdrawing participants         (428,138)      (1,370,831)
                                                 --------------   --------------

Net assets available for benefits per the
Form 5500                                        $ 686,544,794    $ 683,756,508
                                                 ==============   ==============

The  following is a  reconciliation  of benefits  paid to  participants  per the
financial statements to the Form 5500:

                                                     Year Ended December 31,
                                                     2001                2000

Benefits paid to participants per the
 financial statements                             $ 36,247,614    $ 49,542,280
Add:  Amounts allocated to withdrawing
 participants during the current year                  428,138       1,370,831
Less:  Amounts allocated to withdrawing
Participants during the prior year                  (1,370,831)       (250,899)
                                                  -------------   -------------

Benefits paid to participants per the Form 5500   $ 35,304,921    $ 50,662,212
                                                  =============   =============

                                      -10-

Ameren Corporation
Savings Investment Plan

Notes to Financial Statements
December 31, 2001 and 2000
--------------------------------------------------------------------------------


     Amounts allocated to withdrawing participants are recorded on the Form 5500
     for benefit  claims that have been processed and approved for payment prior
     to December 31, 2001 and 2000, as  applicable,  but not yet paid as of that
     date.

7.   Other Matters

     Effective  January 1, 2001, the Plan was amended to merge the assets of the
     Ameren  Corporation  Employee Stock Ownership Plan for Certain Employees of
     CIPS into the Plan.  The  assets  transferred  into the Plan  consisted  of
     436,088  shares of Ameren stock as of the date of the transfer  with a fair
     market value of $20,211,328.

8.   Federal Income Tax Status

     The Plan obtained its latest  determination  letter July 31, 2001, in which
     the Internal  Revenue  Service stated that the Plan was in compliance  with
     the applicable  requirements  of the Internal  Revenue Code. The Company is
     currently  amending the Plan document to reflect changes that are effective
     in 2002. The Company believes that the Plan currently is designed and being
     operated in compliance  with the  applicable  requirements  of the Internal
     Revenue Code and,  therefore,  the Plan  continues to qualify under Section
     401(a) and the related trust  continues to be tax-exempt as of December 31,
     2001.  Therefore,  no provision  for income taxes has been  included in the
     Plan's financial statements.

9.   Subsequent Event

     Effective  June 1, 2002,  with the passage of the  Economic  Growth and Tax
     Relief  Reconciliation Act (EGTRRA),  the Plan was changed to designate the
     Ameren Stock Fund of the Plan as an Employee  Stock  Ownership  Plan and to
     allow all employees a choice  between  dividend  reinvestment  and dividend
     payment on their various Employee Stock Ownership Plan accounts.  Effective
     July 1, 2002,  the Plan was also changed to allow  management  employees to
     contribute  up to 50% of  their  base  pay to the  Plan,  subject  to ERISA
     limitation  requirements,  and the "catch  up"  contribution  provision  of
     EGTRRA for all employees age 50 and older was implemented as well.


                                      -11-





Ameren Corporation                                                                                     Schedule I
Savings Investment Plan


Schedule of Assets (Held at End of Year)
December 31, 2001
----------------------------------------------------------------------------------------------------------------------
(a)            (b)                                            (c)                                           (e)
     Identity of issue, borrower,               Description of investment including
     lessor or similar party                    maturity date, rate of interest,                          Current
                                                collateral, par, or maturity value                         value

                                                                                             

     Massachusetts Funds                        MSIF Trust Fund                                        $124,134,320
     Barclays Global Investment Funds, Inc.     Barclays Global Investors' Equity Index Fund             46,661,437
     The American Funds Group                   Europacific Growth Fund                                  21,609,653
     Vanguard Group                             Vanguard US Growth Fund                                  39,883,621
     Washington Mutual Investments              Washington Mutual Investors Fund                         87,789,899
     Vanguard Group                             Vanguard Asset Allocation Fund                           68,541,101
     Vanguard Group                             Vanguard Extended Market Index Fund                       5,349,502

*    Northern Trust Company                     Short-term Investment Fund                                3,184,174
     T. Rowe Price Stable Asset Management      T. Rowe Price Stable Value Common Trust Fund             85,156,018

*    Ameren Corporation                         Ameren Common Stock Fund                                180,505,606

     Pacific Investment Management Company      MFO Pimco Funds                                           4,522,490

**   Participants                               Participant Loans                                        16,275,294
                                                                                                        -----------
                                                                                                       $683,613,115
                                                                                                       ============


*      Investment represents allowable transaction with a party-in-interest
**     Interest  rates vary from 7.0% to 10.5% and loan maturity dates extend
       from January 2001 through December 2009.
NOTE:  Information pertaining to column (d) was not available for
       nonparticipant-directed investments.







                                   SIGNATURE

     The Plan.  Pursuant to the  requirements of the Securities  Exchange Act of
1934,  the  registrant  has duly caused  this annual  report to be signed on its
behalf by the undersigned hereunto duly authorized.


                                          AMEREN CORPORATION
                                          SAVINGS INVESTMENT PLAN


                                          AMEREN SERVICES COMPANY
                                               (Administrator)



                                          By /s/ Donna K. Martin
                                            ---------------------------
                                                 Donna K. Martin
                                                 Vice President

June 28, 2002




                                  EXHIBIT INDEX

                             Exhibits Filed Herewith
                             -----------------------


Exhibit No.                          Description
----------           -------------------------------------

   23                Consent of Independent Accountants



                                                                     EXHIBIT 23


                       CONSENT OF INDEPENDENT ACCOUNTANTS


We  hereby  consent  to the  incorporation  by  reference  in  the  Registration
Statement on Form S-8 ( Nos.  333-43737 and 333-72156) of Ameren  Corporation of
our report  dated June 27, 2002  relating  to the  financial  statements  of the
Ameren Corporation Savings Investment Plan, which appears in this Form 11-K.


/s/ Pricewaterhouse Coopers LLP
PricewaterhouseCoopers LLP
St. Louis, Missouri
June 27, 2002