Registration No. 333-_____________
================================================================================


                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                         ______________________________

                                    FORM S-4
                             REGISTRATION STATEMENT
                                      Under
                           THE SECURITIES ACT OF 1933
                         ______________________________

                       INTERSTATE POWER AND LIGHT COMPANY
             (Exact name of registrant as specified in its charter)

       Iowa                           4931                        42-0331370
 (State or other          (Primary Standard Industrial        (I.R.S. Employer
  jurisdiction             Classification Code Number)       Identification No.)
of incorporation)

                              Alliant Energy Tower
                               200 First Street SE
                            Cedar Rapids, Iowa 52401
                                 (319) 398-4411
       (Address, including zip code, and telephone number, including area
               code, of registrant's principal executive offices)

                    F. J. Buri                                Copies to:
           Corporate Secretary Benjamin
           Corporate Secretary Benjamin                   F. Garmer, III, Esq.
        Interstate Power and Light Company                  Foley & Lardner
             4902 North Biltmore Lane                  777 East Wisconsin Avenue
             Madison, Wisconsin 53718                 Milwaukee, Wisconsin 53202
                  (608) 458-3311                            (414) 271-2400
(Name, address, including zip code, and telephone
number, including area code, of agent for service)
                      _____________________________________

     Approximate date of commencement of proposed sale of the securities to the
public: Upon consummation of the Exchange Offer referred to herein.
     If the securities being registered on this Form are being offered in
connection with the formation of a holding company and there is compliance with
General Instruction G, check the following box. |_|
     If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, check the following box and
list the Securities Act registration statement number of the earlier effective
registration statement for the same offering. |_|
     If this Form is a post-effective amendment filed pursuant to Rule 462(d)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. |_|
                      _____________________________________

                         CALCULATION OF REGISTRATION FEE


===============================================================================================
                                             Proposed Maximum   Proposed Maximum    Amount of
   Title of Each Class of     Amount to be    Offering Price        Aggregate      Registration
Securities to be Registered    Registered      Per Share(1)      Offering Price         Fee
- -----------------------------------------------------------------------------------------------
                                                                        
8.375% Series B Cumulative     6,000,000          $25.00        $150,000,000        $12,135.00
Preferred Stock, $.01 par        shares
value (2)..................
- -----------------------------------------------------------------------------------------------

(1)......Estimated solely for purposes of determining the registration fee.
(2)......Calculated pursuant to Rule 457(f) under the Securities Act of 1933.
                      _____________________________________

     The Registrant hereby amend this Registration Statement on such date or
dates as may be necessary to delay its effective date until the Registrants
shall file a further amendment which specifically states that this Registration
Statement shall thereafter become effective in accordance with Section 8(a) of
the Securities Act of 1933 or until the Registration Statement shall become
effective on such date as the Commission, acting pursuant to said Section 8(a),
may determine.

================================================================================


                   Subject to Completion, Dated March 28, 2003

Prospectus

                       Interstate Power and Light Company

                                Offer to Exchange
                            All Outstanding Shares of
                   8.375% Series A Cumulative Preferred Stock
                                  for Shares of
                   8.375% Series B Cumulative Preferred Stock
                            _________________________

o    We are offering to exchange registered shares of 8.375% Series B Cumulative
     Preferred Stock for all of our outstanding unregistered shares of 8.375%
     Series A Cumulative Preferred Stock.

o    The exchange offer expires at 11:59 p.m., New York City time, on _______,
     2003, unless we extend it.

o    The terms of the new preferred shares are substantially identical to those
     of the old preferred shares, except that the new preferred shares will not
     have securities law transfer restrictions and registration rights relating
     to the old preferred shares and the new preferred shares will not provide
     for the payment of additional dividends under circumstances relating to the
     timing of the exchange offer.

o    No established trading market for the new preferred shares currently
     exists. The new preferred shares have been approved for listing on the New
     York Stock Exchange under the symbol "IPL Pr B," subject to notice of
     issuance.

o    All old preferred shares that are validly tendered and not validly
     withdrawn will be exchanged.

o    You may withdraw your tender of old preferred shares any time before the
     exchange offer expires.

o    We will not receive any proceeds from the exchange offer.

o    The exchange of preferred shares will not be a taxable event for U.S.
     federal income tax purposes.

     See "Risk Factors" beginning on page 8 for a discussion of risk factors
that you should consider before deciding to exchange your old preferred shares
for new preferred shares.

     Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or determined if this
prospectus is truthful or complete. Any representation to the contrary is a
criminal offense.
                            _________________________

                               ____________, 2003



                                TABLE OF CONTENTS


PROSPECTUS SUMMARY............................................................1

RISK FACTORS..................................................................7

FORWARD-LOOKING STATEMENTS....................................................8

WHERE YOU CAN FIND MORE INFORMATION...........................................9

USE OF PROCEEDS..............................................................10

CAPITALIZATION...............................................................10

THE EXCHANGE OFFER...........................................................11

DESCRIPTION OF THE NEW PREFERRED SHARES......................................20

UNITED STATES FEDERAL INCOME TAX CONSIDERATIONS..............................26

PLAN OF DISTRIBUTION.........................................................27

LEGAL MATTERS................................................................27

EXPERTS......................................................................27

                            _________________________

     In this prospectus, "we," "us" and "our" refer to Interstate Power and
Light Company.

     This prospectus incorporates important business and financial information
about us that is not included in or delivered with this prospectus. We will
provide you without charge upon your request a copy of any documents that we
incorporate by reference, other than exhibits to those documents that are not
specifically incorporated by reference into those documents. You may request a
copy of a document by writing to F. J. Buri, Corporate Secretary, Interstate
Power and Light Company, 4902 North Biltmore Lane, Madison, Wisconsin 53718, or
by calling Mr. Buri at (608) 458-3311. To ensure timely delivery, you must
request the information no later than five business days before the completion
of the exchange offer. Therefore, you must make any request on or before
____________, 2003.



                                       i


                               PROSPECTUS SUMMARY

     The following prospectus summary highlights selected information from this
prospectus and may not contain all of the information that is important to you.
This prospectus includes the specific terms of the preferred stock we are
offering, as well as information regarding our business. We encourage you to
read this prospectus in its entirety.

                       Interstate Power and Light Company

     We are a regulated utility serving customers in Iowa, Minnesota and
Illinois. We are engaged principally in the generation, transmission,
distribution and sale of electric energy to approximately 526,000 customers in
760 communities; the purchase, distribution, transportation and sale of natural
gas to approximately 235,000 customers in 253 communities; and the delivery of
steam services in selected markets. All of our common stock is owned by Alliant
Energy Corporation, a diversified energy-services provider engaged primarily in
regulated utility operations in both the Midwest, including through our company,
and internationally.

     We were formed as a result of the January 1, 2002 merger between IES
Utilities Inc. and Interstate Power Company. Prior to that merger, Alliant
Energy Corporation owned all of the outstanding common stock of both IES
Utilities Inc. and Interstate Power Company.

     We are subject to the jurisdiction of the Iowa Utilities Board, the
Minnesota Public Utilities Commission and the Illinois Commerce Commission with
respect to various portions of our operations. We are also subject to the
jurisdiction of the Federal Energy Regulatory Commission and the Nuclear
Regulatory Commission. Alliant Energy Corporation is a registered public utility
holding company subject to regulation by the Securities and Exchange Commission,
or the SEC, under the Public Utility Holding Company Act of 1935 and is subject
to the regulatory provisions of that Act. We are also subject to some
requirements of that Act.

     Our principal executive offices are located at Alliant Energy Tower, 200
First Street, SE, Cedar Rapids, Iowa 52401 and our telephone number is (319)
786-4411.

                               The Exchange Offer

Old Preferred Shares.................   We sold 6,000,000 shares of our 8.375%
                                        Series A Cumulative Preferred Stock to
                                        the initial purchaser on December 20,
                                        2002. In this prospectus we refer to
                                        those shares of preferred stock as the
                                        old preferred shares. The initial
                                        purchaser resold the old preferred
                                        shares to qualified institutional buyers
                                        pursuant to Rule 144A under the
                                        Securities Act of 1933.

Registration Rights Agreement........   When we sold the old preferred shares,
                                        we entered into a registration rights
                                        agreement with the initial purchaser in
                                        which we agreed, among other things, to
                                        provide to you and all other holders of
                                        the old preferred shares the opportunity
                                        to exchange your unregistered old
                                        preferred shares for a new series of
                                        substantially identical new preferred
                                        shares that we have registered under the
                                        Securities Act. This exchange offer is
                                        being made for that purpose.

New Preferred Shares.................   We are offering to exchange the old
                                        preferred shares for shares of 8.375%
                                        Series B Cumulative Preferred Stock that
                                        have been registered under the
                                        Securities Act. In this prospectus, we
                                        refer to those registered shares as the
                                        new preferred shares. The terms of the
                                        new preferred shares and the old
                                        preferred shares are substantially
                                        identical except:

                                       1


                                        o    the new preferred shares will be
                                             issued in a transaction registered
                                             under the Securities Act;

                                        o    the new preferred shares will not
                                             contain securities law restrictions
                                             on transfer; and

                                        o    the new preferred shares will not
                                             provide for the payment of
                                             additional dividends under
                                             circumstances relating to the
                                             timing of the exchange offer.

The Exchange Offer...................   We are offering to exchange one new
                                        preferred share for each old preferred
                                        share. As of the date of this
                                        prospectus, 6,000,000 old preferred
                                        shares are outstanding. For procedures
                                        for tendering, see "The Exchange Offer--
                                        Procedures for Tendering Old Preferred
                                        Shares."

Expiration Date......................   This exchange offer will expire at 11:59
                                        p.m., New York City time, on ________,
                                        2003, unless we extend it.


Resales of Preferred Shares..........   We believe that the new preferred shares
                                        issued pursuant to the exchange offer in
                                        exchange for old preferred shares may be
                                        offered for resale, resold and otherwise
                                        transferred by you without compliance
                                        with the registration and prospectus
                                        delivery provisions of the Securities
                                        Act if:


                                        o    you are not our "affiliate" within
                                             the meaning of Rule 405 under the
                                             Securities Act;

                                        o    you are acquiring the new preferred
                                             shares in the ordinary course of
                                             your business; and

                                        o    you have not engaged in, do not
                                             intend to engage in, and have no
                                             arrangement or understanding with
                                             any person to participate in, a
                                             distribution of the new preferred
                                             shares.

                                        If you are an affiliate of ours, or are
                                        engaging in or intend to engage in, or
                                        have any arrangement or understanding
                                        with any person to participate in, a
                                        distribution of the new preferred
                                        shares, then:

                                        o    you may not rely on the applicable
                                             interpretations of the staff of the
                                             SEC;

                                        o    you will not be permitted to tender
                                             old preferred shares in the
                                             exchange offer; and

                                        o    you must comply with the
                                             registration and prospectus
                                             delivery requirements of the
                                             Securities Act in connection with
                                             any resale of the old preferred
                                             shares.

                                       2


                                        Each participating broker-dealer that
                                        receives new preferred shares for its
                                        own account under the exchange offer in
                                        exchange for old preferred shares that
                                        were acquired by the broker-dealer as a
                                        result of market-making or other trading
                                        activity must acknowledge that it will
                                        deliver a prospectus in connection with
                                        any resale of the new preferred shares.
                                        See "Plan of Distribution."

                                        Any broker-dealer that acquired old
                                        preferred shares from us may not rely on
                                        the applicable interpretations of the
                                        staff of the SEC and must comply with
                                        registration and prospectus delivery
                                        requirements of the Securities Act
                                        (including being named as a selling
                                        securityholder) in connection with any
                                        resales of the old preferred shares or
                                        the new preferred shares.

Acceptance of Old Preferred Shares      We will accept for exchange any and all
Delivery of New Preferred Shares.....   old preferred shares that are validly
                                        tendered in the exchange offer and not
                                        withdrawn before the offer expires. The
                                        new preferred shares will be delivered
                                        promptly following the exchange offer.

Withdrawal Rights....................   You may withdraw your tender of old
                                        preferred shares at any time before the
                                        exchange offer expires.

Conditions of the Exchange Offer.....   The exchange offer is subject to the
                                        following conditions, which we may
                                        waive:

                                        o    the exchange offer, or the making
                                             of any exchange by a holder of old
                                             preferred shares will not violate
                                             any applicable law or
                                             interpretation by the staff of the
                                             SEC; and

                                        o    no action may be pending or
                                             threatened in any court or before
                                             any governmental agency with
                                             respect to the exchange offer that
                                             may impair our ability to proceed
                                             with the exchange offer.

Consequences of Failure to              If you are eligible to participate in
Exchange.............................   the exchange offer and you do not tender
                                        your old preferred shares, then you will
                                        not have further exchange or
                                        registration rights and you will
                                        continue to hold old preferred shares
                                        subject to restrictions on transfer.

Federal Income Tax Consequences......   The exchange of an old preferred share
                                        for a new preferred share will not be
                                        taxable to a United States holder for
                                        federal income tax purposes.
                                        Consequently, you will not recognize any
                                        gain or loss upon receipt of the new
                                        preferred shares. See "United States
                                        Federal Income Tax Considerations."

Use of Proceeds......................   We will not receive any proceeds from
                                        the exchange offer.


Accounting Treatment.................   We will not recognize any gain or loss
                                        on the exchange of preferred shares. See
                                        "The Exchange Offer -- Accounting
                                        Treatment."

                                       3


Exchange Agent.......................   The Shareowner Services Department of
                                        Alliant Energy Corporation is the
                                        exchange agent. See "The Exchange
                                        Offer--Exchange Agent."

                            The New Preferred Shares

     The following is a brief summary of some terms of the new preferred
shares. For a more complete description of the terms of the new preferred
shares, see "Description of the New Preferred Shares" in this prospectus.

Issuer...............................   Interstate Power and Light Company.

Securities Offered...................   6,000,000 shares of 8.375% Series B
                                        Cumulative Preferred Stock.

Ranking..............................   The new preferred shares will rank
                                        equally with any other series of our
                                        preferred stock with respect to the
                                        payment of dividends and distributions
                                        of assets. The new preferred shares will
                                        rank senior to our common stock with
                                        respect to the payment of dividends and
                                        distributions of assets.

Dividends............................   Dividends on the new preferred shares
                                        will accrue and be cumulative from the
                                        most recent date on which dividends have
                                        been paid on the old preferred shares at
                                        an annual rate of 8.375% or $2.09375 per
                                        share. The dividends will be payable
                                        quarterly on March 15, June 15,
                                        September 15 and December 15 of each
                                        year, beginning on March 15, 2003, when
                                        and as declared by our board of
                                        directors.

Liquidation Preference...............   If we liquidate, dissolve or wind up,
                                        then the holders of the new preferred
                                        shares at the time outstanding will be
                                        entitled to receive $25 per share, plus
                                        an amount equal to accrued and unpaid
                                        dividends, before any distribution of
                                        assets is made to holders of our common
                                        stock or any other class of our stock
                                        ranking junior to the new preferred
                                        shares.

Redemption...........................   We may not redeem the new preferred
                                        shares prior to March 15, 2013. On or
                                        after March 15, 2013, we may redeem the
                                        new preferred shares, at our option, in
                                        whole or in part, upon not less than 45
                                        nor more than 90 days' notice, at a
                                        price of $25 per share, plus an amount
                                        equal to accrued and unpaid dividends.

Maturity.............................   The new preferred shares do not have any
                                        maturity date, and we are not required
                                        to redeem the preferred shares. In
                                        addition, we are not required to set
                                        aside funds to redeem the new preferred
                                        shares. Accordingly, the new preferred
                                        shares will remain outstanding
                                        indefinitely unless we decide to redeem
                                        them.

Voting Rights........................   Holders of shares of new preferred
                                        shares will only be entitled to the
                                        voting rights provided in the amendment
                                        to our restated articles of
                                        incorporation establishing our preferred
                                        stock and as required by Iowa law. See
                                        "Description of the New Preferred
                                        Shares-- Voting Rights."

                                        4


No Conversion Rights.................   The new preferred shares will not be
                                        convertible into shares of any other
                                        class or series of our capital stock or
                                        any other security.

Ratings..............................   Our preferred stock has been assigned a
                                        rating of BBB- by Standard & Poor's
                                        Ratings Service and Baa3 by Moody's
                                        Investors Service, Inc. Ratings are not
                                        a recommendation to buy, sell or hold
                                        the new preferred shares. We cannot give
                                        any assurance that the ratings will be
                                        retained for any time period or that
                                        they will not be revised downward or
                                        withdrawn by the ratings agencies.

Absence of Market for the               The new preferred shares are a new issue
New Preferred Shares.................   of securities with no established
                                        trading market. Accordingly, we cannot
                                        provide any assurance as to the
                                        development or liquidity of any market
                                        for the new preferred shares. See "Plan
                                        of Distribution."

Listing.............................    The new preferred shares have been
                                        approved for listing on the New York
                                        Stock Exchange under the symbol "IPL Pr
                                        B," subject to official notice of
                                        issuance.

Risk Factors........................    See "Risk Factors" and other information
                                        included or incorporated by reference in
                                        this prospectus for a discussion of
                                        factors you should carefully consider
                                        before deciding to exchange your old
                                        preferred shares for new preferred
                                        shares.



                                       5


                         Selected Financial Information

         The selected income statement data for the years ended December 31,
2000, 2001 and 2002 and the selected balance sheet data as of December 31, 2001
and 2002 set forth below were selected or derived from our audited financial
statements and notes. The selected income statement data for the years ended
December 31, 1998 and 1999 and the selected balance sheet data as of December
31, 1998, 1999 and 2000 set forth below were selected or derived from our
unaudited statements of income and balance sheets, which set forth financial
data prepared on the basis of accounting for the merger of IES Utilities Inc.
and Interstate Power Company as a common control merger. The information set
forth below is qualified in its entirety by and should be read in conjunction
with our Management's Discussion and Analysis of Financial Condition and Results
of Operations and our financial statements and related notes incorporated by
reference in this prospectus.




                                                                  Year Ended December 31,
                                          ------------------------------------------------------------------------
                                             1998           1999           2000            2001           2002
                                          -----------    -----------    -----------     -----------    -----------
                                                                  (Dollars in thousands)
                                                                                        
Income Statement Data:

Operating revenues...................     $1,162,819     $1,142,801     $1,234,007      $1,316,250     $1,211,608
Earnings available for common stock           77,278         93,896         99,724          94,656         88,015
Cash dividends declared on common
 stock............................            27,612        120,509         80,339          80,340         81,790

Ratio of Earnings to Fixed Charges
    and Preferred Stock Dividends:              2.65           3.08           3.08            2.86           2.93



                                                                     As of December 31,
                                          ------------------------------------------------------------------------
                                             1998           1999           2000            2001           2002
                                          -----------    -----------    -----------     -----------    -----------
                                                                  (Dollars in thousands)
Balance Sheet Data:

Total assets.........................     $2,446,315     $2,415,068     $2,524,802      $2,426,314     $2,738,406
Long-term obligations, net...........        872,517        836,486        792,323         922,941        902,243





                                       6


                                  RISK FACTORS

     You should carefully consider the risk factors described below, as well as
the other information included or incorporated by reference in this prospectus,
before deciding to exchange your old preferred shares for new preferred shares.
The risks and uncertainties described below are not the only ones facing our
company.

The energy industry is rapidly changing and becoming increasingly competitive,
which may adversely affect our ability to operate profitably.

     The energy industry is in a period of fundamental change resulting from
legislative and regulatory changes. Although we expect that deregulation in our
retail service territories will likely be delayed due to events related to
California's restructured electric utility industry, regulatory changes and
other developments will continue to increase competitive pressures on electric
and gas utility companies. Generally, increased competition could threaten our
market share in some segments of our business and could reduce our profit
margins. Such competitive pressures could cause us to lose customers and incur
additional costs that might not be recovered from customers.

If we are unable to recover the cost of fuel, purchased power and natural gas
from our customers, or if we do not obtain the amount of expected rate relief
requested in our pending rate cases, then we may experience an adverse impact on
the profitability of our business.

     Over 90% of our operating revenues are from our Iowa operations. Our Iowa
operations are entitled, subject to regulatory review, to automatically recover
increases in the cost of fuel, purchased energy and natural gas purchased for
resale through electric and natural gas rates. Purchased power capacity costs in
Iowa are not recovered from electric customers through these energy adjustment
clauses. Recovery of these costs must be addressed in a formal rate proceeding.
We currently have pending two rate cases in Iowa in which we have requested rate
relief of $102 million. We expect to receive final rate relief for these rate
cases by mid-2003. If we do not receive the amount of rate relief that we
expect, the increased rates are not approved on a timely basis or we are
otherwise unable to recover our costs through rates, then we may experience an
adverse impact on our results of operations and cash flows.

Costs of compliance with environmental laws are significant and the costs of
compliance with new environmental laws and the incurrence of environmental
liabilities could adversely affect our profitability.

     Our operations are subject to extensive regulation relating to
environmental protection. To comply with these legal requirements, we must spend
significant sums on environmental monitoring, pollution control equipment and
emission fees. New environmental laws and regulations affecting our operations
may be adopted, and new interpretations of existing laws and regulations could
be adopted or become applicable to us or our facilities, which may substantially
increase environmental expenditures made by us in the future. In addition, we
may not be able to recover all of our costs for environmental expenditures
through electric and natural gas rates in the future. Under current law, we may
also be responsible for any on-site liabilities associated with the
environmental condition of the facilities that we have previously owned or
operated, regardless of whether the liabilities arose before, during or after
the time we owned or operated the facilities. The incurrence of a material
environmental liability could have a material adverse effect on our results of
operations and financial condition.

A downgrade in our credit ratings could negatively affect our access to, and
cost of, capital.

     Our business is capital intensive and the fulfillment of our long-term
strategies depends, at least in part, upon our ability to access capital at
attractive rates and terms. The financial difficulties of many energy companies
and other issues affecting the energy industry have caused the credit ratings
agencies to more thoroughly review the capital structure, cash flows and
earnings potential of energy companies, including us. Standard & Poor's and
Moody's downgraded our credit ratings in December 2002 and January 2003,
respectively. As a result of those downgrades or any future downgrades in our
credit ratings, our borrowing costs may increase and our access to capital may
be limited. If access to capital becomes significantly constrained, then our
financial condition and results of operations could be significantly adversely
affected.

                                       7


                           FORWARD-LOOKING STATEMENTS

     This prospectus, including the information we incorporate by reference,
contains forward-looking statements that are intended to qualify for the safe
harbors from liability established by the Private Securities Litigation Reform
Act of 1995. All statements other than statements of historical fact, including
statements regarding anticipated financial performance, business strategy and
management's plans and objectives for future operations, are forward-looking
statements. These forward-looking statements can be identified as such because
the statements generally include words such as "expect," "intend," "believe,"
"anticipate," "estimate," "plan" or "objective" or other similar expressions.
These forward-looking statements are subject to risks and uncertainties that
could cause actual results to differ materially from those expressed in, or
implied by, these statements. Some, but not all, of the risks and uncertainties
include those described in the "Risk Factors" section of this prospectus and the
following:

     o    weather effects on sales and revenues;

     o    general economic and political conditions in our service territories;

     o    federal and state regulatory and government actions, including issues
          associated with the deregulation of the utility industry, the ability
          to obtain adequate and timely rate relief, the payment of dividends
          and the receipt of necessary approvals for our Power Iowa plan;

     o    unanticipated construction and acquisition expenditures;

     o    issues related to operating and purchased-power and fuel costs that we
          have incurred but cannot recover through increased rates;

     o    unanticipated issues related to the supply and price of purchased
          electricity;

     o    unexpected issues related to the operations of our nuclear facility;

     o    unanticipated costs associated with environmental remediation efforts
          and with environmental compliance generally;

     o    technological developments;

     o    unanticipated costs associated with the risk or occurrence of
          terrorist attacks;

     o    employee workforce factors, including changes in key executives,
          collective bargaining agreements or work stoppages; and

     o    changes in the rate of inflation.


                                       8


                       WHERE YOU CAN FIND MORE INFORMATION

     We file annual, quarterly and current reports and other information with
the SEC. We have also filed a registration statement on Form S-4, including
exhibits, under the Securities Act of 1933 with respect to the securities
offered by this prospectus. This prospectus is a part of the registration
statement, but does not contain all of the information included in the
registration statement or the exhibits. You may read and copy this registration
statement and any other document that we file at the SEC's public reference room
at 450 Fifth Street, N.W., Washington D.C. You can call the SEC at
1-800-SEC-0330 for further information on the operation of the public reference
room. You can also find our public filings with the SEC on the internet at a web
site maintained by the SEC located at http://www.sec.gov.

     We are "incorporating by reference" specified documents that we file with
the SEC, which means:

     o    incorporated documents are considered part of this prospectus;

     o    we are disclosing important information to you by referring you to
          those documents; and

     o    information we file with the SEC will automatically update and
          supersede information contained in this prospectus.

     We incorporate by reference our Annual Report on Form 10-K for the year
ended December 31, 2002 and any future filings we make with the SEC under
Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 after
the date of this prospectus and before the completion of the exchange offer.
Some of these reports, however, are or may be filed on a combined basis with our
parent, Alliant Energy Corporation, and its direct subsidiary, Wisconsin Power
and Light Company. Information contained in these reports relating to these
entities is filed by them on their own behalf and not by us.

     You may request a copy of any of these filings, at no cost, by writing to
F. J. Buri, Corporate Secretary, Interstate Power and Light Company, 4902 North
Biltmore Lane, Madison, Wisconsin 53718, or by calling Mr. Buri at (608)
458-3311.


                                       9


                                 USE OF PROCEEDS

     This exchange offer is intended to satisfy our obligations under the
registration rights agreement entered into in connection with the issuance of
the old preferred shares. We will not receive any cash proceeds from the
issuance of the new preferred shares. We used the net proceeds of approximately
$144.8 million from the sale of the old preferred shares to repay our short-term
debt.

                                 CAPITALIZATION

     The following table sets forth our consolidated capitalization, including
short-term debt, as of December 31, 2002.

                                                      As of December 31, 2002
                                                    ----------------------------
                                                       Actual        % of Total
                                                    ------------    ------------
                                                           (In thousands)

Common stock....................................    $    33,427
Additional paid-in capital......................        477,701
Retained earnings...............................        374,428
Accumulated other comprehensive loss............        (18,887)
                                                    -----------
   Total common equity..........................        866,669            46.4%
Cumulative preferred stock......................        145,100             7.8
Long-term debt (excluding current portion)......        855,389            45.8
                                                    ------------    -----------
      Total capitalization......................    $ 1,867,158           100.0%
                                                    ===========     ===========



                                       10


                               THE EXCHANGE OFFER

Purpose and Effect; Registration Rights

     We sold the old preferred shares on December 20, 2002 in a transaction
exempt from the registration requirements of the Securities Act. Therefore, the
old preferred shares are subject to significant restrictions on resale. In
connection with the issuance of the old preferred shares, we entered into a
registration rights agreement, which required that we:

     o    file with the SEC a registration statement under the Securities Act
          relating to the exchange offer and the issuance and delivery of new
          preferred shares in exchange for the old preferred shares;

     o    use our reasonable best efforts to cause the SEC to declare the
          exchange offer registration statement effective under the Securities
          Act; and

     o    use our reasonable best efforts to consummate the exchange offer on or
          before July 1, 2003.

     If you participate in the exchange offer, you will, with limited
exceptions, receive new preferred shares that are freely tradeable and not
subject to restrictions on transfer. You should read this prospectus under the
heading "-- Resales of New Preferred Shares" for more information relating to
your ability to transfer the new preferred shares.

     If you are eligible to participate in the exchange offer and do not tender
your old preferred shares, then you will continue to hold the untendered old
preferred shares, which will continue to be subject to restrictions on transfer
under the Securities Act.

     The exchange offer is intended to satisfy our exchange offer obligations
under the registration rights agreement. The above summary of the registration
rights agreement is not complete and is subject to, and qualified by reference
to, all the provisions of the registration rights agreement. A copy of the
registration rights agreement has been filed as an exhibit to the registration
statement that includes this prospectus.

Terms of the Exchange Offer

     We are offering to exchange 6,000,000 shares of our 8.375% Series B
Cumulative Preferred Stock that have been registered under the Securities Act
for all of our outstanding unregistered shares of 8.375% Series A Cumulative
Preferred Stock.

     Upon the terms and subject to the conditions set forth in this prospectus
and in the accompanying letter of transmittal, we will accept all old preferred
shares validly tendered and not withdrawn before 11:59 p.m., New York City time,
on the expiration date of the exchange offer. We will issue one new preferred
share in exchange for each outstanding old preferred share we accept in the
exchange offer. You may tender some or all of your preferred shares under the
exchange offer. The exchange offer is not conditioned upon any minimum number of
old preferred shares being tendered.

     The form and terms of the new preferred shares will be the same as the form
and terms of the old preferred shares, except that:

     o    the new preferred shares will be registered with the SEC and thus will
          not be subject to the restrictions on transfer or bear legends
          restricting their transfer;

     o    all of the new preferred shares will be represented by global
          preferred stock certificates in book-entry form unless exchanged for
          shares in definitive certificated form under the limited circumstances
          described under "Description of the New Preferred Shares -- Book-Entry
          Procedures and Form;" and

                                       11


     o    the new preferred shares will not provide for the payment of
          additional dividends under circumstances relating to the timing of the
          exchange offer.

     Dividends on the new preferred shares will accrue and be cumulative from
the most recent date on which dividends have been paid on the old preferred
shares. Accordingly, registered holders of new preferred shares on the record
date for the first dividend payment date following the completion of the
exchange offer will receive dividends accrued and cumulative from the most
recent date on which dividends have been paid on the old preferred shares.
However, if that record date occurs prior to completion of the exchange offer,
then the dividends payable on the first dividend payment date following the
completion of the exchange offer will be paid to the registered holders of the
old preferred shares on that record date.

     In connection with the exchange offer, you do not have any appraisal or
dissenters' rights under the Iowa Business Corporation Act. We intend to conduct
the exchange offer in accordance with the registration rights agreement and the
applicable requirements of the Securities Exchange Act of 1934 and the rules and
regulations of the SEC. The exchange offer is not being made to, nor will we
accept tenders for exchange from, holder of the old preferred shares in any
jurisdiction in which the exchange offer or the acceptance of it would not be in
compliance with the securities or blue sky laws of the jurisdiction.

     We will be deemed to have accepted validly tendered old preferred shares
when we have given oral or written notice of our acceptance to the exchange
agent. The exchange agent will act as agent for the tendering holders for the
purpose of receiving the new preferred shares from us.

     If we do not accept any tendered old preferred shares because of an invalid
tender or for any other reason, then we will return certificates for any
unaccepted old preferred shares without expense to the tendering holder as
promptly as practicable after the expiration date.

Expiration Date; Amendments

     The exchange offer will expire at 11:59 p.m., New York City time, on
________, 2003, unless we, in our sole discretion, extend the exchange offer.

     If we determine to extend the exchange offer, then we will notify the
exchange agent of any extension by oral or written notice and give each
registered holder notice of the extension by means of a press release or other
public announcement before 9:00 a.m., New York City time, on the next business
day after the previously scheduled expiration date.

     We reserve the right, in our sole discretion, to delay accepting any old
preferred shares, to extend the exchange offer or to amend or terminate the
exchange offer if any of the conditions described below under "-- Conditions"
have not been satisfied or waived by giving oral or written notice to the
exchange agent of the delay, extension, amendment or termination. Further, we
reserve the right, in our sole discretion, to amend the terms of the exchange
offer in any manner. We will notify you as promptly as practicable of any
extension, amendment or termination. We will also file a post-effective
amendment to the registration statement of which this prospectus is a part with
respect to any fundamental change in the exchange offer.

Procedures for Tendering Old Preferred Shares

     Any tender of old preferred shares that is not withdrawn prior to the
expiration date will constitute a binding agreement between the tendering holder
and us upon the terms and subject to the conditions set forth in this prospectus
and in the accompanying letter of transmittal. A holder who wishes to tender old
preferred shares in the exchange offer must do either of the following:

     o    properly complete, sign and date the letter of transmittal, including
          all other documents required by the letter of transmittal; have the
          signature on the letter of transmittal guaranteed if the letter of
          transmittal so requires; and deliver that letter of transmittal and
          other required documents to the


                                       12


          exchange agent at the address listed below under "-- Exchange Agent"
          on or before the expiration date; or

     o    if the old preferred shares are tendered under the book-entry transfer
          procedures described below, transmit to the exchange agent on or
          before the expiration date an agent's message.

     In addition, one of the following must occur:

     o    the exchange agent must receive certificates representing your old
          preferred shares along with the letter of transmittal on or before the
          expiration date, or

     o    the exchange agent must receive a timely confirmation of book-entry
          transfer of the old preferred shares into the exchange agent's account
          at The Depository Trust Company of New York, or DTC, under the
          procedure for book-entry transfers described below along with the
          letter of transmittal or a properly transmitted agent's message, on or
          before the expiration date; or

     o    the holder must comply with the guaranteed delivery procedures
          described below.

     The term "agent's message" means a message, transmitted by a book-entry
transfer facility to and received by the exchange agent and forming a part of
the book-entry confirmation, which states that the book-entry transfer facility
has received an express acknowledgement from the tendering DTC participant
stating that the participant has received and agrees to be bound by the letter
of transmittal and that we may enforce the letter of transmittal against the
participant.

     The method of delivery of old preferred shares, the letter of transmittal
and all other required documents to the exchange agent is at your election and
risk. Rather than mail these items, we recommend that you use an overnight or
hand delivery service. In all cases, you should allow sufficient time to assure
timely delivery to the exchange agent before the expiration date. Do not send
letters of transmittal or old preferred shares to us.

     Generally, an eligible institution must guarantee signatures on a letter of
transmittal or a notice of withdrawal unless the old preferred shares are
tendered:

     o    by a registered holder of the old preferred shares who has not
          completed the box entitled "Special Issuance Instructions" or "Special
          Delivery Instructions" on the letter of transmittal; or

     o    for the account of an eligible institution.

     If signatures on a letter of transmittal or a notice of withdrawal are
required to be guaranteed, the guarantee must be by a firm which is:

     o    a member of a registered national securities exchange;

     o    a member of the National Association of Securities Dealers, Inc.;

     o    a commercial bank or trust company having an office or correspondent
          in the United States; or

     o    another "eligible institution" within the meaning of Rule l7Ad-15
          under the Securities Exchange Act.

     If the letter of transmittal is signed by a person other than the
registered holder of any outstanding old preferred shares, then the original
shares must be endorsed or accompanied by appropriate powers of attorney. The
power of attorney must be signed by the registered holder exactly as the
registered holder(s) name(s) appear(s) on the old preferred shares and an
eligible institution must guarantee the signature on the power of attorney.

                                       13


     If the letter of transmittal or any old preferred shares or powers of
attorney are signed by trustees, executors, administrators, guardians,
attorneys-in-fact, officers of corporations or others acting in a fiduciary or
representative capacity, these persons should so indicate when signing. Unless
waived by us, they should also submit evidence satisfactory to us of their
authority to so act.

     If you wish to tender old preferred shares that are registered in the name
of a broker, dealer, commercial bank, trust company or other nominee, then you
should promptly instruct the registered holder to tender on your behalf. If you
wish to tender on your behalf, then you must, before completing the procedures
for tendering old preferred shares, either register ownership of the old
preferred shares in your name or obtain a properly completed bond power from the
registered holder. The transfer of registered ownership may take considerable
time.

     We will determine in our sole discretion all questions as to the validity,
form, eligibility, including time of receipt, and acceptance of old preferred
shares tendered for exchange. Our determination will be final and binding on all
parties. We reserve the absolute right to reject any and all tenders of old
preferred shares not properly tendered or old preferred shares our acceptance of
which might, in the judgment of our counsel, be unlawful. We also reserve the
absolute right to waive any defects, irregularities or conditions of tender as
to any particular old preferred shares. Our interpretation of the terms and
conditions of the exchange offer, including the instructions in the letter of
transmittal, will be final and binding on all parties. Unless waived, any
defects or irregularities in connection with tenders of old preferred shares
must be cured within the time period we determine. Neither we, the exchange
agent nor any other person will incur any liability for failure to give you
notification of defects or irregularities with respect to tenders of your old
preferred shares.

     By tendering, you will represent to us that:

     o    any new preferred shares that the holder receives will be acquired in
          the ordinary course of its business;

     o    the holder has no arrangement or understanding with any person or
          entity to participate in the distribution of the new preferred shares;

     o    if the holder is not a broker-dealer, that it is not engaged in and
          does not intend to engage in the distribution of the new preferred
          shares;

     o    if the holder is a broker-dealer, that the holder's old senior notes
          were acquired as a result of market-making activities or other trading
          activities (see "Plan of Distribution"); and

     o    the holder is not our "affiliate," as defined in Rule 405 of the
          Securities Act, or, if the holder is our affiliate, it will comply
          with any applicable registration and prospectus delivery requirements
          of the Securities Act.

     If any holder or any such other person is our "affiliate," or is engaged in
or intends to engage in or has an arrangement or understanding with any person
to participate in a distribution of the new preferred shares to be acquired in
the exchange offer, then that holder or any such other person:

     o    may not rely on the applicable interpretations of the staff of the
          SEC;

     o    is not entitled and will not be permitted to tender old preferred
          shares in the exchange offer; and

     o    must comply with the registration and prospectus delivery requirements
          of the Securities Act in connection with any resale transaction.

     Each broker-dealer who acquired its old preferred shares as a result of
market-making activities or other trading activities and thereafter receives new
preferred shares issued for its own account in the exchange offer, must
acknowledge that it will deliver a prospectus in connection with any resale of
such new preferred shares issued in


                                       14


the exchange offer. The letter of transmittal states that by so acknowledging
and by delivering a prospectus, a broker-dealer will not be deemed to admit that
it is an "underwriter" within the meaning of the Securities Act. See "Plan of
Distribution" for a discussion of the exchange and resale obligations of
broker-dealers in connection with the exchange offer.

     Any broker-dealer that acquired old preferred shares directly from us may
not rely on the applicable interpretations of the staff of the SEC and must
comply with the registration and delivery requirements of the Securities Act
(including being named as a selling securityholder) in connection with any
resales of the old preferred shares or the new preferred shares.

Acceptance of Old Preferred Shares for Exchange; Delivery of New Preferred
Shares

     Upon satisfaction of all conditions to the exchange offer, we will accept,
promptly after the expiration date, all old preferred shares properly tendered
and will issue the new preferred shares promptly after acceptance of the old
preferred shares.

     For purposes of the exchange offer, we will be deemed to have accepted
properly tendered old preferred shares for exchange when we have given oral or
written notice of that acceptance to the exchange agent. For each old preferred
share accepted for exchange, you will receive a new preferred share having the
same rights and preferences as the old preferred share.

     In all cases, we will issue new preferred shares for old preferred shares
that we have accepted for exchange under the exchange offer only after the
exchange agent timely receives:

     o    certificates for your old preferred shares or a timely confirmation of
          book-entry transfer of your old preferred shares into the exchange
          agent's account at DTC; and

     o    a properly completed and duly executed letter of transmittal and all
          other required documents or a properly transmitted agent's message.

     If we do not accept any tendered old preferred shares for any reason set
forth in the terms of the exchange offer, then we will return the unaccepted old
preferred shares without expense to you. In the case of old preferred shares
tendered by book-entry transfer into the exchange agent's account at DTC under
the book-entry procedures described below, we will credit the unaccepted old
preferred shares to your account maintained with DTC.

Book-Entry Transfer

     We understand that the exchange agent will make a request within two
business days after the date of this prospectus to establish accounts for the
old preferred shares at DTC for the purpose of facilitating the exchange offer,
and any financial institution that is a participant in DTC's system may make
book-entry delivery of old preferred shares by causing DTC to transfer the old
preferred shares into the exchange agent's account at DTC in accordance with
DTC's procedures for transfer. Although delivery of old preferred shares may be
effected through book-entry transfer at DTC, the exchange agent must receive a
properly completed and duly executed letter of transmittal with any required
signature guarantees, or an agent's message instead of a letter of transmittal,
and all other required documents at its address listed below under "-- Exchange
Agent" on or before the expiration date, or if you comply with the guaranteed
delivery procedures described below, within the time period provided under those
procedures.

Guaranteed Delivery Procedures

     If you wish to tender your old preferred shares and your old preferred
shares are not immediately available, or you cannot deliver your old preferred
shares, the letter of transmittal or any other required documents or comply with
DTC's procedures for transfer before the expiration date, then you may
participate in the exchange offer if:

     o    the tender is made through an eligible institution;

                                       15


     o    before the expiration date, the exchange agent receives from the
          eligible institution a properly completed and duly executed notice of
          guaranteed delivery, substantially in the form provided by us, by
          facsimile transmission, mail or hand delivery, containing:

          o    the name and address of the holder and the principal amount of
               old preferred shares tendered,

          o    a statement that the tender is being made thereby, and

          o    a guarantee that within three New York Stock Exchange trading
               days after the expiration date, the certificates representing the
               old preferred shares in proper form for transfer or a book-entry
               confirmation and any other documents required by the letter of
               transmittal will be deposited by the eligible institution with
               the exchange agent; and

     o    the exchange agent receives the properly completed and executed letter
          of transmittal as well as certificates representing all tendered old
          preferred shares in proper form for transfer, or a book-entry
          confirmation, and all other documents required by the letter of
          transmittal within three New York Stock Exchange trading days after
          the expiration date.

Withdrawal Rights

     You may withdraw your tender of old preferred shares at any time before the
exchange offer expires.

     For a withdrawal to be effective, the exchange agent must receive a written
notice of withdrawal at its address listed below under "-- Exchange Agent." The
notice of withdrawal must:

     o    specify the name of the person who tendered the old preferred shares
          to be withdrawn;

     o    identify the old preferred shares to be withdrawn, or, in the case of
          old preferred shares tendered by book-entry transfer, the name and
          number of the DTC account to be credited, and otherwise comply with
          the procedures of DTC; and

     o    if certificates for old preferred shares have been transmitted,
          specify the name in which those old preferred shares are registered if
          different from that of the withdrawing holder.

     If you have delivered or otherwise identified to the exchange agent the
certificates for old preferred shares, then, before the release of these
certificates, you must also submit the serial numbers of the particular
certificates to be withdrawn and a signed notice of withdrawal with the
signatures guaranteed by an eligible institution, unless the holder is an
eligible institution.

     We will determine in our sole discretion all questions as to the validity,
form and eligibility, including time of receipt, of notices of withdrawal. Our
determination will be final and binding on all parties. Any old preferred shares
so withdrawn will be deemed not to have been validly tendered for purposes of
the exchange offer. We will return any old preferred shares that have been
tendered but that are not exchanged for any reason to the holder, without cost,
as soon as practicable after withdrawal, rejection of tender or termination of
the exchange offer. In the case of old preferred shares tendered by book-entry
transfer into the exchange agent's account at DTC, the old preferred shares will
be credited to an account maintained with DTC for the old preferred shares. You
may retender properly withdrawn old preferred shares by following one of the
procedures described under "-- Procedures for Tendering Old Preferred Shares" at
any time on or before the expiration date.

                                       16


Conditions

     Notwithstanding any other term of the exchange offer, we will not be
required to accept for exchange, or to exchange new preferred shares for, any
old preferred shares if:

     o    the exchange offer, or the making of any exchange by a holder of old
          preferred shares, would violate any applicable law or applicable
          interpretation by the staff of the SEC; or

     o    any action or proceeding is instituted or threatened in any court or
          by or before any governmental agency with respect to the exchange
          offer which, in our judgment, would reasonably be expected to impair
          our ability to proceed with the exchange offer.

     The conditions listed above are for our sole benefit and we may assert them
regardless of the circumstances giving rise to any condition. Subject to
applicable law, we may waive these conditions in our discretion in whole or in
part at any time and from time to time. If we waive these conditions, then we
intend to continue the exchange offer for at least five business days after the
waiver. If we fail at any time to exercise any of the above rights, the failure
will not be deemed a waiver of those rights, and those rights will be deemed
ongoing rights which may be asserted at any time and from time to time.

Exchange Agent

     The Shareowner Services Department of Alliant Energy Corporation is the
exchange agent for the exchange offer. You should direct any questions and
requests for assistance and requests for additional copies of this prospectus,
the letter of transmittal or the notice of guaranteed delivery to the exchange
agent addressed as follows:

         By Registered or Certified Mail:

         Shareowner Services Department of Alliant Energy Corporation
         P.O. Box 2568
         4902 North Biltmore Lane
         Madison, Wisconsin  53701-2568

         By Hand or Overnight Courier:

         Shareowner Services Department of Alliant Energy Corporation
         4902 North Biltmore Lane
         Madison, Wisconsin  53718

         By Facsimile:

         (608) 458-3321

     Delivery of the letter of transmittal to an address other than as listed
above or transmission via facsimile other than as listed above will not
constitute a valid delivery of the letter of transmittal.

Fees and Expenses

     We will pay the expenses of the exchange offer. We will not make any
payments to brokers, dealers or others soliciting acceptances of the exchange
offer. We are making the principal solicitation by mail; however, our officers
and employees may make additional solicitations by facsimile transmission,
e-mail, telephone or in person. You will not be charged a service fee for the
exchange of your preferred shares, but we may require you to pay any transfer or
similar government taxes in certain circumstances.

                                       17


Transfer Taxes

     You will not be obligated to pay any transfer taxes, unless you instruct us
to register new preferred shares in the name of, or request that old preferred
shares not tendered or not accepted in the exchange offer be returned to, a
person other than the registered tendering holder.

Accounting Treatment

     We will record the new preferred shares at the same carrying values as the
old preferred shares, which is the aggregate stated value of the old preferred
shares, as reflected in our accounting records on the date of exchange.
Accordingly, we will not recognize any gain or loss on the exchange of preferred
shares. We will charge the expenses of this offer to additional paid-in capital.

Consequences of Failure to Exchange Old Preferred Shares

     If you are eligible to participate in the exchange offer but do not tender
your old preferred shares, you will not have any further registration rights,
except in limited circumstances with respect to specific types of holders of old
preferred shares. Old preferred shares that are not tendered or are tendered but
not accepted will, following the consummation of the exchange offer, continue to
be subject to the existing restrictions on transfer set forth in the legend on
the old preferred shares and in the offering memorandum dated December 18, 2002,
relating to the old preferred shares. Accordingly, you may resell the old
preferred shares that are not exchanged only:

     o    to us;

     o    so long as the old preferred shares are eligible for resale under Rule
          144A under the Securities Act, to a person whom you reasonably believe
          is a "qualified institutional buyer" within the meaning of Rule 144A
          purchasing for its own account or for the account of a qualified
          institutional buyer in a transaction meeting the requirements of Rule
          144A;

     o    in accordance with another exemption from the registration
          requirements of the Securities Act; or

     o    under an effective registration statement under the Securities Act;

in each case in accordance with all other applicable securities laws. We do not
intend to register the old preferred shares under the Securities Act.

     Old preferred shares that are not exchanged in the exchange offer will
remain outstanding and continue to accrue dividends and will be entitled to the
rights and benefits their holders have under our restated articles of
incorporation relating to the old preferred shares.

Resales of New Preferred Shares

     Based on interpretations of the staff of the SEC, as set forth in no-action
letters to third parties, we believe that new preferred shares issued under the
exchange offer in exchange for old preferred shares may be offered for resale,
resold and otherwise transferred by any holder of old preferred shares without
further registration under the Securities Act and without delivery of a
prospectus that satisfies the requirements of Section 10 of the Securities Act
if:

     o    the holder is not our "affiliate" within the meaning of Rule 405 under
          the Securities Act;

     o    the new preferred shares are acquired in the ordinary course of the
          holder's business; and

     o    the holder does not intend to participate in a distribution of the new
          preferred shares.

                                       18


     Any holder who exchanges old preferred shares in the exchange offer with
the intention of participating in any manner in a distribution of the new
preferred shares must comply with the registration and prospectus delivery
requirements of the Securities Act in connection with a secondary resale
transaction.

     This prospectus may be used for an offer to resell, resale or other
retransfer of new preferred shares. With regard to broker-dealers, only
broker-dealers that acquire the old preferred shares as a result of
market-making activities or other trading activities may participate in the
exchange offer. Each broker-dealer that receives new preferred shares for its
own account in exchange for old preferred shares, where the old preferred shares
were acquired by the broker-dealer as a result of market-making activities or
other trading activities, must acknowledge that it will deliver a prospectus in
connection with any resale of the new preferred shares. Please see "Plan of
Distribution" for more details regarding the transfer of new preferred shares.




                                       19


                     DESCRIPTION OF THE NEW PREFERRED SHARES

General

     Our total authorized capital stock as set forth in our restated articles of
incorporation consists of 40,000,000 shares, of which 24,000,000 are designated
common stock, par value $2.50 per share, and 16,000,000 shares are designated
preferred stock, par value $.01 per share. As of the date of this prospectus,
our outstanding common stock consists of 13,370,788 shares, all of which are
owned by our parent corporation, Alliant Energy Corporation. As of the date of
this prospectus, our outstanding preferred stock consists of 6,000,000 shares of
preferred stock designated as "8.375% Series A Cumulative Preferred Stock."

     Under our restated articles of incorporation, our board of directors may
establish one or more series of preferred stock to be issued out of authorized
preferred stock. Our board of directors, without approval of our shareowners,
may determine the rights and preferences of the shares of preferred stock of any
series so established. Pursuant to this authority, we will issue up to 6,000,000
shares of our preferred stock designated as "8.375% Series B Cumulative
Preferred Stock" in the exchange offer. When issued and exchanged for the old
preferred shares in the manner described in this prospectus, the new preferred
shares will be validly issued, fully paid and nonassessable.

     The terms of the preferred stock are contained in an amendment to our
restated articles of incorporation. We refer to the old preferred shares and the
new preferred shares collectively as the preferred stock. The following is a
summary of the terms of the preferred stock. This summary does not purport to be
complete and is subject to and qualified in its entirety by reference to the
amendment to our restated articles of incorporation, which is filed as an
exhibit to the registration statement of which this prospectus is a part and
incorporated by reference into this prospectus. See "Where You Can Find More
Information." We urge you to read the amendment to our articles of incorporation
that will establish our preferred stock because it, and not this summary,
defines your rights as a holder of our preferred stock.

Ranking

     The preferred stock will rank senior to our common stock and to any other
of our equity securities that we may issue in the future that by their terms
rank junior to the preferred stock with respect to payment of dividends and
distribution of assets upon our liquidation, dissolution or winding up. The
preferred stock will rank on a parity to any other of our preferred stock that
we may later authorize or issue with respect to payment of dividends and
distribution of assets upon our liquidation, dissolution or winding up.

Dividends

     The holders of shares of our preferred stock will be entitled to receive,
when, as and if declared by our board of directors out of funds legally
available for the payment of dividends, cash dividends at an annual rate of
8.375% of the liquidation preference. Dividends on the preferred stock will
accrue and be cumulative from the date of original issuance subject to the
following. Dividends on the new preferred shares will accrue and be cumulative
from the most recent date on which dividends have been paid on the old preferred
shares. Accordingly, registered holders of new preferred shares on the record
date for the first dividend payment date following the completion of the
exchange offer will receive dividends accrued and cumulative from the most
recent date on which dividends have been paid on the old preferred shares.
However, if that record date occurs prior to completion of the exchange offer,
then the dividends payable on the first dividend payment date following the
completion of the exchange offer will be paid to the registered holders of the
old preferred shares on that record date. Dividends will be payable quarterly in
arrears on March 15, June 15, September 15 and December 15 of each year. If any
of those dates is not a business day, then dividends will be payable on the next
succeeding business day. Dividends will be payable on those dates to holders of
record as they appear in our stock records at the close of business on the
applicable record date, which will be the last business day of the month prior
to the month in which the applicable dividend payment date falls. The amount of
dividends payable for the initial dividend period or any period shorter than a
full dividend period will be computed on the basis of a 360-day year consisting
of twelve 30-day months and the actual number of days elapsed in the period.

                                       20


     Our board of directors will not authorize, and we will not pay, any
dividends on our preferred stock or set aside funds for the payment of dividends
if the terms of any of our agreements, including agreements relating to our
indebtedness, prohibit that authorization, payment or setting aside of funds or
provide that the authorization, payment or setting aside of funds is a breach of
or a default under that agreement, or if the authorization, payment or setting
aside of funds is restricted or prohibited by law. We are and may in the future
become a party to agreements which restrict or prevent the payment of dividends
on, or the purchase or redemption of, shares. These restrictions may be
indirect, for example, covenants requiring us to maintain specified levels of
net worth or assets, or direct. We do not believe that these restrictions
currently have any adverse impact on our ability to pay dividends on our
preferred stock.

     Notwithstanding the foregoing, dividends on our preferred stock will accrue
whether or not we have earnings, whether or not there are funds legally
available for the payment of dividends and whether or not dividends are
authorized. Accrued but unpaid dividends on our preferred stock will not bear
interest, and holders of our preferred stock will not be entitled to any
dividends in excess of full cumulative dividends as described above. We will
credit any dividend made on our preferred stock first to the earliest accrued
and unpaid dividend due. We will not pay any dividends on our common stock or
any other of our equity securities that by their terms rank junior to our
preferred stock with respect to payment of dividends if dividends payable on our
preferred stock are in arrears.

Liquidation Preference

     Upon any voluntary or involuntary liquidation, dissolution or winding up of
our company, each holder of shares of our preferred stock will be entitled to
payment, out of our assets available for distribution, of an amount equal to the
$25 liquidation preference per share of our preferred stock held by that holder.
In addition, such holder will be entitled to payment of an amount equal to all
accrued and unpaid dividends on those shares to, but excluding, the date of
liquidation, dissolution or winding up. The holders of our preferred stock are
entitled to these payments before any distribution is made on any junior stock,
including our common stock. After payment in full of the liquidation preference
and the amount equal to all accrued and unpaid dividends to which holders of
shares of our preferred stock are entitled, the holders will not be entitled to
any further participation in any distribution of our assets. If upon any
voluntary or involuntary liquidation, dissolution or winding up of our company,
the amounts payable with respect to shares of our preferred stock and any other
outstanding series of preferred stock ranking on a parity with our preferred
stock are not paid in full, then the holders of shares of our preferred stock
and the holders of the parity stock will share equally and ratably in any
distribution of our assets in proportion to the full distributable amounts to
which each such holder is entitled.

     Neither the voluntary sale, conveyance, exchange or transfer, for cash,
shares of stock, securities or other consideration, of all or substantially all
of our property or assets nor the consolidation, merger or amalgamation of our
company with or into any other entity or the consolidation, merger or
amalgamation of any other entity with or into our company will be deemed to be a
voluntary or involuntary liquidation, dissolution or winding up of our company.

Redemption

     We may not redeem the preferred stock prior to March 15, 2013. On or after
March 15, 2013, we may redeem the preferred stock, at our option, in whole or in
part from time to time, upon not less than 45 nor more than 90 days' notice, at
a price of $25 per share, plus an amount equal to accrued and unpaid dividends
to, but excluding, the redemption date.

Maturity

     The preferred stock does not have any maturity date, and we are not
required to redeem the preferred stock. In addition, we are not required to set
aside funds to redeem the preferred stock. Accordingly, the preferred stock will
remain outstanding indefinitely unless we decide to redeem them.

                                       21


Voting Rights

     Our preferred stock will have no voting rights except as set forth below or
as otherwise provided by Iowa law. In the event that any four quarterly
cumulative dividends, whether consecutive or not, payable on our preferred stock
are in arrears, the holders of our preferred stock will have the right, voting
separately as a class together with holders of any other series of preferred
stock ranking on a parity with our preferred stock issued pursuant to this
prospectus as to payment of dividends, and upon which like voting rights have
been conferred and are exercisable, at the next meeting of shareowners called
for the election of directors, to elect two members of our board of directors.
The right of such holders of our preferred stock to elect members of our board
of directors will continue until such time as all dividends accumulated and in
arrears on such shares of preferred stock have been paid in full, at which time
such right will terminate, subject to revesting in the event of each and every
subsequent failure to pay dividends as described above. Upon any termination of
the right of the holders of our preferred stock to vote as a class for
directors, the term of office of all directors then in office elected by such
holders voting as a class will terminate immediately.

     Without the affirmative vote or consent of the holders of at least
two-thirds of the outstanding shares of our preferred stock, voting as a single
class, or voting as a single class together with holders of any other series of
preferred stock upon which like voting or consent rights have been conferred and
which are similarly affected by the matter to be voted upon, we may not:

     o    increase the amount of preferred stock authorized under our restated
          articles of incorporation or create or issue any class of stock in
          addition to the class of preferred stock authorized under our restated
          articles of incorporation ranking senior to or on a parity with the
          class of preferred stock currently authorized under our restated
          articles of incorporation, or any series thereof, as to the payment of
          dividends or the distribution of assets;

     o    adopt any amendment to our restated articles of incorporation that
          adversely alters the preferences, powers and rights of our preferred
          stock;

     o    issue any shares of preferred stock of any series if the cumulative
          dividends payable on our preferred stock are in arrears; or

     o    create or issue any shares of preferred stock of any series that rank
          senior to our preferred stock as to payment of dividends or the
          distribution of assets.

     On any matter described above in which the holders of our preferred stock
are entitled to vote as a class, such holders will be entitled to one vote per
share. On any other matter for which holders of our preferred stock are provided
the right to vote together with holders of our common stock under Iowa law, if
any, holders of our preferred stock will be entitled to the number of votes per
share determined by dividing the liquidation preference of such share by 100.

Conversion Rights

     The holders of the preferred stock will not have any rights to convert
shares of the preferred stock into shares of any other class or series of our
capital stock or any other security.

Transfer Agent

     The transfer agent and registrar for our preferred stock is the Shareowner
Services Department of Alliant Energy Corporation, P.O. Box 2568, 4902 North
Biltmore Lane, Madison, Wisconsin 53701-2568.

Book-Entry Procedures and Form

     The Depository Trust Company of New York City, or DTC, will act as
securities depository for the preferred stock. The preferred stock will be
issued only as fully-registered securities registered in the name of a


                                       22


nominee of DTC, in each case for credit to an account of a direct or indirect
participant in DTC as described below. One or more fully-registered global
preferred stock certificates, representing the total aggregate number of shares
of preferred stock, will be issued to and deposited with DTC.

     Purchases of preferred stock under the DTC system must be made by or
through participants, who will receive a credit for the preferred stock on DTC's
records. DTC will then record on the participants' and indirect participants'
records the ownership interest of each actual purchaser, or beneficial owner, of
each share of preferred stock. DTC will not provide written confirmation of
purchases to beneficial owners, but participants or indirect participants
through which the beneficial owners purchased the preferred stock should provide
the beneficial owners with written confirmations providing details of the
transactions, as well as period statements of the beneficial owners' holdings.
Transfers of ownership interests in preferred stock are to be accomplished by
entries made on the books of participants acting on behalf of beneficial owners.
Unless the use of the book-entry system for the preferred stock is discontinued,
beneficial owners will not receive certificates representing their ownership
interests in the preferred stock.

     The laws of some states may require that some persons take physical
delivery in certificated form of specified securities, such as the preferred
stock, that they own. Consequently, the ability to transfer beneficial interests
in a global security to these persons will be limited to that extent. Because
DTC can act only on behalf of participants, which in turn act on behalf of
indirect participants and various banks, the ability of a person having
beneficial interests in a global security to pledge their interests to persons
or entities that do not participate in this system, or otherwise take actions in
respect of those interests, may be affected by the lack of a physical
certificate evidencing their interests.

     Except as described below, owners of beneficial interests in the global
preferred stock will not be entitled to have preferred stock registered in their
names, will not receive or be entitled to receive physical delivery of preferred
stock in certificated form and will not be considered the registered owners or
holders thereof for any purpose.

     DTC has no knowledge of the actual beneficial owners of the preferred
stock. DTC's records reflect only the identity of the participants to whose
accounts the preferred stock is credited, which persons may or may not be the
beneficial owners. The participants and indirect participants will remain
responsible for keeping account of their holdings on behalf of their customers.

     So long as DTC or its nominee is the registered owner or holder of a global
preferred stock certificate, DTC or its nominee, as the case may be, is the sole
owner or holder of the preferred stock represented by the global preferred stock
certificate for all purposes. No beneficial owner of an interest in a global
preferred stock certificate can transfer that interest except in accordance with
DTC's applicable procedures.

     Conveyance of notices and other communications by DTC to participants, by
participants to indirect participants, and by participants and indirect
participants to beneficial owners will be governed by arrangements among them,
subject to any statutory or regulatory requirements as may be in effect from
time to time.

     Redemption notices, if applicable, in respect of any preferred stock held
in book-entry form will be sent to DTC. If less than all of the preferred stock
is being redeemed, DTC will determine the amount of the interest of each
participant to be redeemed in accordance with its procedures.

     Neither DTC or its nominee will itself consent or vote with respect to the
shares of preferred stock. Under its usual procedures, DTC will mail an omnibus
proxy to us as soon as possible after the record date. The omnibus proxy will
assign the consenting or voting rights of DTC's nominee to the direct
participants to whose accounts the shares of preferred stock are credited on the
record date.

     We will make payments in respect of the global preferred stock certificates
registered in the name of DTC or its nominee to DTC in its capacity as the
registered holder. We will treat the persons in whose names the preferred stock,
including the global preferred stock certificates, are registered as the owners
of the preferred stock for the purpose of receiving the payments and for any and
all other purposes. Consequently, neither we nor any of


                                       23


our agents has or will have any responsibility or liability for any aspect of
DTC's records or any participant's or indirect participant's records relating to
or payments made on account of beneficial ownership interests in the global
preferred stock certificates, or for maintaining, supervising or reviewing any
of DTC's records of any participant's or indirect participant's records relating
to the beneficial ownership interests in the global preferred stock
certificates. We will pay any redemption proceeds, distributions and dividend
payments on the shares of preferred stock to a nominee of DTC. DTC has advised
us that, upon DTC's receipt of funds and corresponding detail information from
us or an agent, DTC will credit participants' accounts on payable date in
accordance with their respective holdings as shown on DTC's records. Payments by
participants to beneficial owners will be governed by standing instructions and
customary practices, as is the case with securities held for the accounts of
customers in bearer form or registered in "street name," and will be the
responsibility of the participant and not of DTC, any agent or us, subject to
statutory or regulatory requirements as may be in effect from time to time.
Payment of redemption proceeds, distributions and dividends to a nominee of DTC
is the responsibility of us or any agent. Any disbursement of payments to direct
participants is the responsibility of DTC and disbursement of any payments to
the beneficial owners is the responsibility of the direct and indirect
participants.

     DTC has advised us that:

     o    DTC is a limited-purpose trust company organized under the New York
          Banking Law, a "banking organization" within the meaning of the New
          York Banking Law, a member of the Federal Reserve System, a "clearing
          corporation" within the meaning of the New York Uniform Commercial
          Code and a "clearing agency" registered under Section 17A of the
          Securities Exchange Act of 1934;

     o    DTC holds securities that its direct participants deposit with DTC and
          facilitates the settlement among direct participants of securities
          transactions, such as transfers and pledges, in deposited securities
          through electronic computerized book-entry changes in direct
          participants' accounts, thereby eliminating the need for physical
          movement of securities certificates;

     o    direct participants include securities brokers and dealers, trust
          companies, clearing corporations and other organizations;

     o    DTC is owned by a number of its direct participants and by the New
          York Stock Exchange, Inc., the American Stock Exchange LLC and the
          National Association of Securities Dealers, Inc.;

     o    access to the DTC system is also available to indirect participants
          such as securities brokers and dealers, banks and trust companies that
          clear through or maintain a custodial relationship with a direct
          participant, either directly or indirectly; and

     o    the rules applicable to DTC and its direct and indirect participants
          are on file with the SEC.

     Although DTC has agreed to the foregoing procedures in order to facilitate
transfers of interests in the global preferred stock certificates among
participants of DTC, it is under no obligation to perform such procedures, and
such procedures may be discontinued at any time. None of us or any of our
respective agents will have any responsibility for the performance by DTC or its
participants or indirect participants of their respective obligations under the
rules and procedures governing their operations, including maintaining,
supervising or reviewing the records relating to, payments made on account of,
or beneficial ownership interests in, global preferred stock certificates.

     According to DTC, the foregoing information with respect to DTC has been
provided to its participants and other members of the financial community for
informational purposes only and is not intended to serve as a representation,
warranty or contract modification of any kind. We have provided the foregoing
descriptions of the operations and procedures of DTC solely as a matter of
convenience. DTC's operations and procedures are solely within DTC's control and
are subject to change by DTC from time to time. Neither we nor the initial
purchaser take any responsibility for these operations or procedures, and you
are urged to contact DTC or its participants directly to discuss these matters.

                                       24


Certificated Preferred Stock

     We will issue shares of preferred stock in certificated form in exchange
for global preferred stock certificates if:

     o    DTC or any successor depository notifies us that it is unwilling or
          unable to continue as a depository for the global preferred stock
          certificates or ceases to be a "clearing agency" registered under the
          Securities Exchange Act of 1934 and a successor depository is not
          appointed by us within 90 days of such notice; or

     o    we determine that the preferred stock will no longer be represented by
          global preferred stock certificates.




                                       25


                 UNITED STATES FEDERAL INCOME TAX CONSIDERATIONS

     This summary is of a general nature and is included herein solely for
informational purposes. It is not intended to be, nor should it be construed as
being, legal or tax advice. No representation with respect to the consequences
to any particular purchaser of the preferred stock is made. Prospective
purchasers should consult their own tax advisors with respect to their
particular circumstances.

     The following is a summary of certain material United States federal income
tax consequences to a beneficial owner of preferred stock (a "United States
Holder") who is:

     o    a citizen or resident of the United States;

     o    a corporation or other entity treated as a corporation for United
          States federal income tax purposes created or organized in or under
          the laws of the United States, any state thereof or the District of
          Columbia;

     o    an estate whose income is subject to United States federal income tax
          regardless of its source; or

     o    a trust if a court within the United States is able to exercise
          primary supervision over the administration of the trust and one or
          more United States persons have the authority to control all
          substantial decisions of the trust or if the trust has made a valid
          election to be treated as a United States person.

     The following summary deals only with preferred stock held as capital
assets by purchasers at the issue price who are United States Holders and not
with special classes of holders, such as dealers in securities or currencies,
financial institutions, life insurance companies, tax-exempt entities, persons
holding preferred stock as part of a hedge, conversion, constructive sale
transaction, straddle or other risk reduction strategy, persons who hold their
preferred stock through partnerships and other passthrough entities and persons
whose functional currency is not the U.S. dollar. Persons considering the
purchase of preferred stock should consult their own tax advisors concerning
these matters and as to the tax treatment under foreign, state and local tax
laws and regulations. We cannot provide any assurance that the Internal Revenue
Service will not challenge the conclusions stated below. We have not sought and
will not seek a ruling from the IRS on any of the matters discussed below.

     This summary is based upon the Internal Revenue Code of 1986, Treasury
Regulations, IRS rulings and pronouncements and judicial decisions now in
effect, all of which are subject to change at any time. Changes in this area of
law may be applied retroactively in a manner that could cause the income tax
consequences to vary substantially from the consequences described below,
possibly adversely affecting a United States Holder. The authorities on which
this discussion is based are subject to various interpretations, and it is
therefore possible that the federal income tax treatment of the exchange of the
old preferred shares for the new preferred shares may differ from the treatment
described below.

     The exchange of old preferred shares for the new preferred shares under the
terms of the exchange offer should not constitute a taxable exchange. As a
result:

     o    A holder should not recognize taxable gain or loss as a result of
          exchanging old preferred shares for the new preferred shares under the
          terms of the exchange offer;

     o    The holder's holding period of the new preferred shares should include
          the holding period of the old preferred shares exchanged for the new
          preferred shares; and

     A holder's adjusted tax basis in the new preferred shares should be the
same as the adjusted tax basis, immediately before the exchange, of the old
preferred shares exchanged for the new preferred shares.

                                       26


                              PLAN OF DISTRIBUTION

     If you are a broker-dealer and hold old preferred shares for your own
account as a result of market-making activities or other trading activities and
you receive new preferred shares in exchange for old preferred shares in the
exchange offer, then you may be a statutory underwriter and must acknowledge
that you will deliver a prospectus in connection with any resale of the new
preferred shares. This prospectus, as it may be amended or supplemented from
time to time, may be used by a broker-dealer in connection with resales of new
preferred shares received in exchange for old preferred shares where the shares
of such old preferred shares were acquired as a result of market-making
activities or other trading activities. Unless you are a broker-dealer, you must
acknowledge that you are not engaged in, do not intend to engage in, and have no
arrangement or understanding with any person to participate in a distribution of
new preferred shares. We have agreed that we will make this prospectus, as
amended or supplemented, available to any broker-dealer for use in connection
with any such resale.

     We will not receive any proceeds in connection with the exchange offer or
any sale of new preferred shares by broker-dealers. New preferred shares
received by broker-dealers for their own account pursuant to the exchange offer
may be sold from time to time in one or more transactions in the
over-the-counter market, in negotiated transactions, through the writing of
options on the new preferred shares or a combination of these methods of resale,
at market prices prevailing at the time of resale, at prices related to such
prevailing market prices or negotiated prices. Any resale may be made directly
to purchasers or to or through brokers or dealers who may receive compensation
in the form of commissions or concessions from any such broker-dealers or the
purchasers of any shares of such new preferred shares. Any broker-dealer that
resells new preferred shares that were received by it for its own account
pursuant to the exchange offer and any broker-dealer that participates in a
distribution of such new preferred shares may be deemed to be an "underwriter"
within the meaning of the Securities Act and any profit on any such resale of
new preferred shares and any commissions or concessions received by any such
persons may be deemed to be underwriting compensation under the Securities Act.
The letter of transmittal states that by acknowledging that it will deliver, and
by delivering, a prospectus, a broker-dealer will not be deemed to admit that it
is an "underwriter" within the meaning of the Securities Act. See "The Exchange
Offer - Resales of the New Preferred Shares."

                                  LEGAL MATTERS

     The validity of the new preferred shares will be passed upon by Foley &
Lardner.

                                     EXPERTS

     The consolidated financial statements and the related financial statement
schedule of Interstate Power and Light Company incorporated in this registration
statement by reference from Interstate Power and Light Company's Annual Report
on Form 10-K for the year ended December 31, 2002 have been audited by Deloitte
& Touche LLP, independent auditors, as stated in their report, and have been so
incorporated in reliance upon the report of such firm given upon their authority
as experts in accounting and auditing.

                                       27







                       Interstate Power and Light Company






                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 20.  Indemnification of Directors and Officers.

     The Iowa Business Corporation Act ("IBCA") grants each corporation
organized thereunder, such as the Registrant, the power to indemnify its
directors and officers against liabilities for certain of their acts. The
Registrant's Restated Articles of Incorporation provide that the Registrant
shall indemnify its directors and officers to the fullest extent permitted by
the IBCA and may, but is not required to, purchase and maintain insurance on
behalf of any person who is or was a director, officer, employee or agent of the
Registrant, or is or was serving at the request of the Registrant as a director,
officer, employee or agent of another corporation, partnership, joint venture,
trust or other enterprise against any liability asserted and incurred against
such person in any such capacity or arising out of such person's status as such,
whether or not the Registrant would have the power to indemnify such person
against such liability under the provisions thereof. The Registrant's Bylaws
permit the Registrant to maintain such insurance and further provide that the
Registrant shall indemnify directors and officers of the Registrant to the full
extent permitted by the IBCA and advance any and all reasonable expenses
incurred in any proceeding to which any such director or officer is a party
because he or she is or was a director or officer.

     Under the IBCA, directors of the Registrant are not subject to personal
liability to the Registrant or its shareowners for acts or failures to act
except under certain circumstances. In addition, the IBCA grants corporations
organized thereunder, such as the Registrant, the authority to adopt a provision
in their respective articles of incorporation eliminating or limiting, with
certain exceptions, the personal liability of a director to the corporation or
to its shareowners for monetary damages for certain breaches of fiduciary duty
as a director. The Registrant's Restated Articles of Incorporation eliminates
the personal liability of each director except for liability (i) for any breach
of the director's duty of loyalty to the Registrant or its shareowners, (ii) for
acts or omissions not in good faith or which involve any intentional misconduct
or knowing violation of the law, (iii) for any transaction from which the
director derived an improper personal benefit, or (iv) under Section 490.833 of
the IBCA relating to liability for unlawful distribution.

     The foregoing statements are subject to the detailed provisions of the IBCA
and the Restated Articles of Incorporation and Bylaws of the Registrant and
should be read in conjunction therewith for a more full understanding of their
effect on the Registrant.

     The indemnification provided by the Registrant is not exclusive of any
other rights to which a director or officer of the Registrant may be entitled.
The Registrant also carries directors' and officers' liability insurance. The
Registrant's directors' and officers' insurance policies are designed to
reimburse the Registrant for any payments made by it pursuant to the foregoing
indemnification provisions.

     The Registration Rights Agreement contains provisions under which the
initial purchaser agrees to indemnify the directors and officers of the
Registrant against certain liabilities, including liabilities under the
Securities Act of 1933 or to contribute to payments the directors and officers
may be required to make in respect thereof.

Item 21.  Exhibits and Financial Statement Schedules.

     (a)  Exhibits. The exhibits listed in the accompanying Exhibit Index are
filed (except where otherwise indicated) as part of this Registration Statement.

     (b)  Financial Statement Schedules. Schedule II - Valuation and Qualifying
Accounts is hereby incorporated by reference to the Registrant's Annual Report
on Form 10-K for the year ended December 31, 2002 (File No. 1-3632). All other
schedules are omitted because they are not applicable or not require, or because
the required information is shown either in the consolidated financial
statements or in the notes thereto.

     (c)  Reports, Opinions or Appraisals. Not applicable.

                                      II-1


Item 22.  Undertakings.

     (a)  The Registrant hereby undertakes:

          (1)  To file, during any period in which offers or sales are being
     made, a post-effective amendment to this Registration Statement:

               (i)   To include any prospectus required by Section 10(a)(3) of
          the Securities Act of 1933;

               (ii)  To reflect in the prospectus any facts or events arising
          after the effective date of the Registration Statement (or the most
          recent post-effective amendment thereof) which, individually or in the
          aggregate, represent a fundamental change in the information set forth
          in the Registration Statement. Notwithstanding the foregoing, any
          increase or decrease in volume of securities offered (if the total
          dollar value of securities offered would not exceed that which was
          registered) and any deviation from the low or high end of the
          estimated maximum offering range may be reflected in the form of
          prospectus filed with the Commission pursuant to Rule 424(b) if, in
          the aggregate, the changes in volume and price represent no more than
          a 20% change in the maximum aggregate offering price set forth in the
          "Calculation of Registration Fee" table in the effective Registration
          Statement;

               (iii) To include any material information with respect to the
          plan of distribution not previously disclosed in the Registration
          Statement or any material change to such information in the
          Registration Statement.

          (2)  That, for the purpose of determining any liability under the
     Securities Act of 1933, each such post-effective amendment shall be deemed
     to be a new Registration Statement relating to the securities offered
     therein, and the offering of such securities at that time shall be deemed
     to be the initial bona fide offering thereof.

          (3)  To remove from registration by means of a post-effective
     amendment any of the securities being registered which remain unsold at the
     termination of the offering.

     (b)  The Registrant hereby undertakes that, for purposes of determining any
liability under the Securities Act of 1933, each filing of the Registrant's
annual report pursuant to Section 13(a) or Section 15(d) of the Securities
Exchange Act of 1934 that is incorporated by reference in the Registration
Statement shall be deemed to be a new Registration Statement relating to the
securities offered therein, and the offering of such securities at that time
shall be deemed to be the initial bona fide offering thereof.

     (c)  Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Securities Act of 1933 and is, therefore, unenforceable. In the event
that a claim for indemnification against such liabilities (other than the
payment by a Registrant of expenses incurred or paid by a director, officer or
controlling person of a Registrant in the successful defense of any action, suit
or proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.

     (d)  The Registrant hereby undertakes to respond to requests for
information that is incorporated by reference into the Prospectus pursuant to
Item 4, 10(b), 11 or 13 of this Form, within one business day of receipt of such
request, and to send the incorporated documents by first class mail or other
equally prompt means. This includes information contained in documents filed
subsequent to the effective date of the Registration Statement through the date
of responding to the request.

     (e)  The Registrant hereby undertakes to supply by means of a
post-effective amendment all information concerning a transaction, and the
company being acquired involved therein, that was not the subject of and
included in the Registration Statement when it became effective.

                                      II-2


                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant
has duly caused this Registration Statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Madison, State of
Wisconsin, on March 28, 2003.

                                     INTERSTATE POWER AND LIGHT COMPANY


                                     By: /s/ Erroll B. Davis, Jr.
                                        ----------------------------------------
                                         Erroll B. Davis, Jr.
                                         Chairman and Chief Executive Officer

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.

       Signature                           Title                       Date


/s/ Erroll B. Davis, Jr.         Chairman, Chief Executive        March 28, 2003
- ----------------------------     Officer and Director
Erroll B. Davis, Jr.             (Principal Executive Officer)


/s/ Thomas M. Walker             Executive Vice President and     March 28, 2003
- ----------------------------     Chief Financial Officer
Thomas M. Walker                 (Principal Financial Officer)

/s/ John E. Kratchmer            Vice President, Controller       March 28, 2003
- ----------------------------     and Chief Accounting
John E. Kratchmer                Officer (Principal
                                 Accounting Officer)

          *                      Director                         March 28, 2003
- ----------------------------
Alan B. Arends

          *                      Director                         March 28, 2003
- ----------------------------
Jack B. Evans

          *                      Director                         March 28, 2003
- ----------------------------
Joyce L. Hanes

          *                      Director                         March 28, 2003
- ----------------------------
Lee Liu

          *                      Director                         March 28, 2003
- ----------------------------
Katharine C. Lyall

          *                      Director                         March 28, 2003
- ----------------------------
Singleton B. McAllister

          *                      Director                         March 28, 2003
- ----------------------------
David A. Perdue

          *                      Director                         March 28, 2003
- ----------------------------
Judith D. Pyle

                                       S-1


          *                      Director                         March 28, 2003
- ----------------------------
Robert W. Schlutz

          *                      Director                         March 28, 2003
- ----------------------------
Wayne H. Stoppelmoor

                  *              Director                         March 28, 2003
Anthony R. Weiler

*By: /s/ Erroll B. Davis, Jr.
     -----------------------
     Erroll B. Davis, Jr.
     Attorney-in-fact



                                      S-2


                                  EXHIBIT INDEX

Exhibit
Number                        Document Description
- -------                       --------------------

(4.1)     Restated Articles of Incorporation of Interstate Power and Light
          Company ("IP&L") (incorporated by reference to Exhibit 3.1 to IP&L's
          Form 10-Q for the quarter ended September 30, 2002).

(4.2)     Articles of Amendment to the Restated Articles of Incorporation of
          IP&L (incorporated by reference to Exhibit 3.5a to IP&L's Form 10-K
          for the year ended December 31, 2002).

(4.3)     Registration Rights Agreement, dated as of December 20, 2002, between
          IP&L and Robert W. Baird & Co. Incorporated (incorporated by reference
          to Exhibit 4.18 to IP&L's Form 10-K for the year ended December 31,
          2002).

(4.4)     Indenture of Mortgage and Deed of Trust, dated as of September 1,
          1993, between IP&L and Bank One Trust Company, National Association
          ("Bank One Trust"), successor, as Trustee (incorporated by reference
          to Exhibit 4(c) to IP&L's Form 10-Q for the quarter ended September
          30, 1993), and the indentures supplemental thereto dated,
          respectively, October 1, 1993, November 1, 1993, March 1, 1995,
          September 1, 1996 and April 1, 1997 (Exhibit 4(d) in IP&L's Form 10-Q
          dated November 12, 1993, Exhibit 4(e) in IP&L's Form 10-Q dated
          November 12, 1993, Exhibit 4(b) in IP&L's Form 10-Q dated May 12,
          1995, Exhibit 4(c)(i) in IP&L's Form 8-K dated September 19, 1996 and
          Exhibit 4(a) in IP&L's Form 10-Q dated May 14, 1997).

(4.5)     Indenture of Mortgage and Deed of Trust, dated as of August 1, 1940,
          between IP&L and Bank One Trust, successor, as Trustee (incorporated
          by reference to Exhibit 2(a) to IP&L's Registration Statement, File
          No. 2-25347), and the indentures supplemental thereto dated,
          respectively, March 1, 1941, July 15, 1942, August 2, 1943, August 10,
          1944, November 10, 1944, August 8, 1945, July 1, 1946, July 1, 1947,
          December 15, 1948, November 1, 1949, November 10, 1950, October 1,
          1951, March 1, 1952, November 5, 1952, February 1, 1953, May 1, 1953,
          November 3, 1953, November 8, 1954, January 1, 1955, November 1, 1955,
          November 9, 1956, November 6, 1957, November 4, 1958, November 3,
          1959, November 1, 1960, January 1, 1961, November 7, 1961, November 6,
          1962, November 5, 1963, November 4, 1964, November 2, 1965, September
          1, 1966, November 30, 1966, November 7, 1967, November 5, 1968,
          November 1, 1969, December 1, 1970, November 2, 1971, May 1, 1972,
          November 7, 1972, November 7, 1973, September 10, 1974, November 5,
          1975, July 1, 1976, November 1, 1976, December 1, 1977, November 1,
          1978, December 1, 1979, November 1, 1981, December 1, 1980, December
          1, 1982, December 1, 1983, December 1, 1984, March 1, 1985, March 1,
          1988, October 1, 1988, May 1, 1991, March 1, 1992, October 1, 1993,
          November 1, 1993, March 1, 1995, September 1, 1996 and April 1, 1997
          (Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 2(a) in File No. 2-25347,
          Exhibit 2(a) in File No. 2-25347, Exhibit 4.10 in IP&L's Form 10-K for
          the year 1966, Exhibit 4.10 in IP&L's Form 10-K for the year 1966,
          Exhibit 4.10 in IP&L's Form 10-K for the year 1967, Exhibit 4.10 in
          IP&L's Form 10-K for the year 1968, Exhibit 4.10 in IP&L's Form 10-K
          for the year 1969, Exhibit 1 in IP&L's Form 8-K dated December 1970,
          Exhibit 2(g) in File No. 2-43131, Exhibit 1 in IP&L's Form 8-K dated
          May 1972, Exhibit 2(i) in File No. 2-56078, Exhibit 2(j) in File No.
          2-56078, Exhibit 2(k) in File No. 2-56078, Exhibit 2(l) in File No.
          2-56078, Exhibit 1 in IP&L's


                                       E-1

                                  EXHIBIT INDEX
Exhibit
Number                        Document Description
- -------                       --------------------

          Form 8-K dated July 1976, Exhibit 1 in IP&L's Form 8-K dated December
          1976, Exhibit 2(o) in File No. 2-60040, Exhibit 1 in IP&L's Form 10-Q
          dated June 30, 1979, Exhibit 2(q) in Form S-16 in File No. 2-65996,
          Exhibit 2 in IP&L's Form 10-Q dated March 31, 1982, Exhibit 4(s) in
          IP&L's Form 10-K for the year 1981, Exhibit 4(t) in IP&L's Form 10-K
          for the year 1982, Exhibit 4(u) in IP&L's Form 10-K for the year 1983,
          Exhibit 4(v) in IP&L's Form 10-K for the year 1984, Exhibit 4(w) in
          IP&L's Form 10-K for the year 1984, Exhibit 4(b) in IP&L's Form 10-Q
          dated May 12, 1988, Exhibit 4(c) in IP&L's Form 10-Q dated November
          10, 1988, Exhibit 4(d) in IP&L's Form 10-Q dated August 13, 1991,
          Exhibit 4(c) in IP&L's Form 10-K for the year 1991, Exhibit 4(a) in
          IP&L's Form 10-Q dated November 12, 1993, Exhibit 4(b) in IP&L's Form
          10-Q dated November 12, 1993, Exhibit 4(a) in IP&L's Form 10-Q dated
          May 12, 1995, Exhibit 4(f) in IP&L's Form 8-K dated September 19, 1996
          and Exhibit 4(b) in IP&L's Form 10-Q dated May 14, 1997).

(4.6)     Indenture or Deed of Trust dated as of February 1, 1923, between IP&L
          and Bank One Trust, successor, and Lawrence Dillard, successor, as
          Trustees (incorporated by reference to Exhibit B-1 to File No.
          2-1719), and the indentures supplemental thereto dated, respectively,
          May 1, 1940, May 2, 1940, October 1, 1945, October 2, 1945, January 1,
          1948, September 1, 1950, February 1, 1953, October 2, 1953, August 1,
          1957, September 1, 1962, June 1, 1967, February 1, 1973, February 1,
          1975, July 1, 1975, September 2, 1975, March 10, 1976, February 1,
          1977, January 1, 1978, March 1, 1979, March 1, 1980, May 31, 1986,
          July 1, 1991, September 1, 1992 and December 1, 1994 (Exhibit B-1-k in
          File No. 2-4921, Exhibit B-1-l in File No. 2-4921, Exhibit 7(m) in
          File No. 2-8053, Exhibit 7(n) in File No. 2-8053, Exhibit 7(o) in File
          No. 2-8053, Exhibit 4(e) in File No. 33-3995, Exhibit 4(b) in File No.
          2-10543, Exhibit 4(q) in File No. 2-10543, Exhibit 2(b) in File No.
          2-13496, Exhibit 2(b) in File No. 2-20667, Exhibit 2(b) in File No.
          2-26478, Exhibit 2(b) in File No. 2-46530, Exhibit 2(aa) in File No.
          2-53860, Exhibit 2(bb) in File No. 2-54285, Exhibit 2(bb) in File No.
          2-57510, Exhibit 2(cc) in File No. 2-57510, Exhibit 2(ee) in File No.
          2-60276, Exhibit 2 in File No. 0-849, Exhibit 2 in File No. 0-849,
          Exhibit 2 in File No. 0-849, Exhibit 4(g) in File No. 33-3995, Exhibit
          4(h) in File No. 0-849, Exhibit 4(m) in File No. 0-849 and Exhibit
          4(f) in File No. 0-4117-1).

(4.7)     Indenture (For Unsecured Subordinated Debt Securities), dated as of
          December 1, 1995, between IP&L and Bank One Trust, successor, as
          Trustee (incorporated by reference to Exhibit 4(i) to IP&L's Amendment
          No. 1 to Registration Statement, File No. 33-62259).

(4.8)     Indenture (For Senior Unsecured Debt Securities), dated as of August
          1, 1997, between IP&L and Bank One Trust, successor, as Trustee
          (incorporated by reference to Exhibit 4(j) to IP&L's Registration
          Statement, File No. 333-32097).

(4.9)     Officers' Certificate, dated as of August 4, 1997, creating IP&L's
          6-5/8% Senior Debentures, Series A, due 2009 (incorporated by
          reference to Exhibit 4.12 to IP&L's Annual Report on Form 10-K for the
          year ended December 31, 2000).

(4.10)    Officers' Certificate, dated as of March 6, 2001, creating IP&L's
          6-3/4% Senior Debentures, Series B, due 2011 (incorporated by
          reference to Exhibit 4 to IP&L's Form 8-K, dated March 6, 2001).

(4.11)    The Original through the Nineteenth Supplemental Indentures of IP&L,
          successor, to JPMorgan Chase Bank and James P. Freeman, successor, as
          Trustee, dated January 1, 1948 securing First Mortgage Bonds
          (incorporated by reference to Exhibits 4(b) through 4(t) to Interstate
          Power Company's ("IPC") Registration Statement No. 33-59352 dated
          March 11, 1993).


                                       E-2

                                  EXHIBIT INDEX
Exhibit
Number                        Document Description
- -------                       --------------------

(4.12)    Twentieth Supplemental Indenture of IP&L, successor, to JPMorgan Chase
          Bank and James P. Freeman, successor, as Trustees, dated May 15, 1993
          (incorporated by reference to Exhibit 4(u) to IPC's Registration
          Statement No. 33-59352 dated March 11, 1993). (4.13) Twenty-First
          Supplemental Indenture of IP&L, successor, to JPMorgan Chase Bank and
          James P. Freeman, as Trustees, dated December 31, 2001 (incorporated
          by reference to Exhibit 4.3 to IP&L's Form 8-K, dated January 1,
          2002). Pursuant to Item 601(b)(4)(iii) of Regulation S-K, the
          Registrant agrees to furnish to the Securities and Exchange
          Commission, upon request, any instrument defining the rights of
          holders of long-term debt not being registered that is not filed as an
          exhibit to this Registration Statement on Form S-4. No such instrument
          authorizes securities in excess of 10% of the total assets of the
          Registrant.

(5)       Opinion of Foley & Lardner (including consent of counsel).

(12)      Statement re computation of ratios of earnings to fixed charges and
          preferred stock dividends.

(23.1)    Consent of Deloitte & Touche, LLP.

(23.2)    Consent of Foley & Lardner (filed as part of Exhibit (5)).

(24)      Powers of attorney.

(99.1)    Form of Letter of Transmittal.

(99.2)    Form of Notice of Guaranteed Delivery.

(99.3)    Guidelines for Certification of Taxpayer Identification Number on Form
          W-9.

(99.4)    Form of Letter to Clients.

(99.5)    Form of Instructions to Registered Holder and/or DTC Participant from
          Beneficial Owners.

(99.6)    Form of Letter to Nominees.

Documents incorporated by reference to filings made by IP&L under the Securities
Exchange Act of 1934, as amended, are under File No. 0-4117-1. Documents
incorporated by reference to filings made by IPC under the Securities Exchange
Act of 1934, as amended, are under File No. 1-3632.


                                      E-3