FOLEY & LARDNER

                                ATTORNEYS AT LAW

CHICAGO                           FIRSTAR CENTER                      SACRAMENTO
DENVER                      777 EAST WISCONSIN AVENUE                  SAN DIEGO
JACKSONVILLE             MILWAUKEE, WISCONSIN 53202-5367           SAN FRANCISCO
LOS ANGELES                  TELEPHONE (414) 271-2400                TALLAHASSEE
MADISON                      FACSIMILE (414) 297-4900                      TAMPA
MILWAUKEE                                                       WASHINGTON, D.C.
ORLANDO                                                          WEST PALM BEACH

                                December 15, 1999

Alliant Energy Resources, Inc.
Alliant Energy Corporation
222 West Washington Avenue
Madison, Wisconsin  53703

Ladies and Gentlemen:

          We have  acted as  counsel  for  Alliant  Energy  Resources,  Inc.,  a
Wisconsin  corporation  (the  "Company"),  and  Alliant  Energy  Corporation,  a
Wisconsin  corporation  and the parent  corporation  of the Company (the "Parent
Guarantor"),  in connection with the preparation of a Registration  Statement on
Form  S-4,   including  the   Prospectus   constituting   a  part  thereof  (the
"Registration  Statement"),  to  be  filed  with  the  Securities  and  Exchange
Commission under the Securities Act of 1933, as amended (the "Securities  Act"),
relating to an offer to exchange (the "Exchange Offer") the Company's new 7 3/8%
Senior Notes due 2009 (the "New Senior Notes") for an equal principal  amount of
the  Company's  outstanding 7 3/8% Senior Notes due 2009 (the  "Existing  Senior
Notes"). The New Senior Notes will be fully and unconditionally  guaranteed (the
"New Senior Note Guarantees") by the Parent Guarantor.

          The Existing  Senior Notes were issued,  and the New Senior Notes will
be  issued,  pursuant  to an  Indenture,  dated  as of  November  4,  1999  (the
"Indenture"), among the Company, the Parent Guarantor and Firstar Bank, N.A., as
Trustee (the "Trustee"),  as supplemented and amended by the First  Supplemental
Indenture,  dated as of November 4, 1999 (the "Supplemental  Indenture"),  among
the Company, the Parent Guarantor and the Trustee.

          In connection with our opinion, we have examined: (a) the Registration
Statement,  including the  Prospectus;  (b) the  Indenture and the  Supplemental
Indenture (included as Exhibits 4.1 and 4.2,  respectively,  to the Registration
Statement);  (c) the  form of the  New  Senior  Notes  and the New  Senior  Note
Guarantees (included as Exhibit 4.3 to the Registration Statement); and (d) such
other  proceedings,  documents and records as we have deemed necessary to enable
us to render this opinion.

          In our examination of the above referenced documents,  we have assumed
the  genuineness  of  all  signatures,   the   authenticity  of  all  documents,
certificates  and  instruments

<PAGE>

Foley & Lardner
Alliant Energy Resources, Inc.
Alliant Energy Corporation
December 15, 1999
Page 2


submitted  to us as  originals  and the  conformity  with the  originals  of all
documents submitted to us as copies.

          Based  upon  the  foregoing,  assuming  that  the  Indenture  and  the
Supplemental Indenture have been duly authorized, executed and delivered by, and
represent  the  valid and  binding  obligation  of,  the  Trustee,  and when the
Registration  Statement,  including any  amendments  thereto,  shall have become
effective  under  the  Securities  Act and the  Indenture  and the  Supplemental
Indenture  shall have been duly qualified under the Trust Indenture Act of 1939,
as amended, and having regard for such legal considerations as we deem relevant,
we are of the opinion that:

          1. The New Senior  Notes,  when duly  executed and  delivered by or on
behalf  of the  Company  in the  form  contemplated  by the  Indenture  and  the
Supplemental  Indenture  upon the  terms  set  forth in the  Exchange  Offer and
authenticated  by the  Trustee,  will be legally  issued  and valid and  binding
obligations of the Company enforceable in accordance with their terms; and

          2. The New Senior Note Guarantees, when duly executed and delivered by
or on behalf of the Parent  Guarantor in the form  contemplated by the Indenture
and the  Supplemental  Indenture upon the terms set forth in the Exchange Offer,
will be legally issued and valid and binding obligations of the Parent Guarantor
enforceable in accordance with their terms;

except,  in each case,  as  enforcement  thereof  may be limited by  bankruptcy,
insolvency, fraudulent transfer, reorganization,  moratorium or other comparable
laws affecting the enforcement of creditors' rights generally or the application
of equitable principles (regardless of whether such enforceability is considered
in a  proceeding  in  equity  or at  law)  and  subject,  in each  case,  to the
qualification  that certain  provisions thereof may be unenforceable in whole or
in part  under the laws of the State of  Wisconsin,  but the  inclusion  of such
provisions  does not affect the validity of the New Senior Notes or the New Note
Senior  Guarantees and each of them contain legally adequate  provisions for the
realization of the principal legal rights and benefits afforded thereby.

          We hereby  consent  to the  reference  to our firm  under the  caption
"Legal  Matters" in the  Prospectus  which is filed as part of the  Registration
Statement,  and to the filing of this opinion as an exhibit to such Registration
Statement.  In giving this consent, we do not admit that we are "experts" within
the  meaning of  Section 11 of the  Securities  Act or within  the  category  of
persons whose consent is required by Section 7 of the Securities Act.

                                         Very truly yours,

                                         /s/ Foley & Lardner

                                         FOLEY & LARDNER