FOLEY & LARDNER

                                ATTORNEYS AT LAW

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                                                            CLIENT/MATTER NUMBER
                                                                     031613/0121
                                December 15, 1999



Alliant Energy Corporation
222 West Washington Avenue
Madison, Wisconsin  53703

Ladies and Gentlemen:

          We have acted as counsel for Alliant Energy  Corporation,  a Wisconsin
corporation  (the   "Company"),   in  conjunction  with  the  preparation  of  a
Registration Statement on Form S-8 (the "Registration Statement") to be filed by
the Company with the Securities and Exchange Commission under the Securities Act
of 1933, as amended (the "Securities Act"),  relating to 2,800,000 shares of the
Company's Common Stock, $.01 par value (the "Common Stock"),  and related Common
Share Purchase Rights (the "Rights"),  which may be issued or acquired  pursuant
to the Alliant Energy  Corporation  Long-Term  Equity Incentive Plan, as amended
(the  "Plan").  The terms of the Rights are as set forth in that certain  Rights
Agreement,  dated as of January 20, 1999, by and between the Company and Firstar
Bank, N. A. (the "Rights Agreement").

          As such counsel, we have examined: (i) the Plan; (ii) the Registration
Statement;  (iii) the Rights Agreement;  (iv) the Company's Restated Articles of
Incorporation and By-Laws,  as amended to date; (v) resolutions of the Company's
Board  of  Directors  relating  to the  Plan  and  the  issuance  of  securities
thereunder;  and  (vi)  such  other  documents  and  records  as we have  deemed
necessary to enable us to render this opinion.

          Based upon the foregoing, we are of the opinion that:

          1. The Company is a corporation validly existing under the laws of the
State of Wisconsin.

          2. The shares of Common Stock,  when issued by the Company pursuant to
the terms and  conditions of the Plan,  will be validly  issued,  fully paid and
nonassessable  and no personal  liability will attach to the ownership  thereof,
except with respect to wage claims of, or other debts owing to, employees of the
Company for services performed, but not exceeding six months' service in any one
case,  as  provided  in  Section   180.0622(2)(b)  of  the  Wisconsin   Business
Corporation Law.



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



          3.  The  Rights  when  issued  pursuant  to the  terms  of the  Rights
Agreement will be validly issued.

          We  consent  to  the  use  of  this  opinion  as  an  exhibit  to  the
Registration  Statement.  In giving  our  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 said Act.

                                        Very truly yours,

                                        /s/ Foley & Lardner

                                        FOLEY & LARDNER