Exhibit 8(b)

                            Fredrikson & Byron, P.A.
                           1100 International Centre
                            900 Second Avenue South
                             Minneapolis, MN 55402
                                 (612) 347-7000




                                 January 8, 2002

Richfield State Agency, Inc.
6625 Lyndale Avenue South
Richfield, Minnesota 55423

     RE:  Agreement and Plan of Merger by and between Richfield State Agency,
          Inc. and Marshall & Ilsley Corporation dated as of November 18, 2001

Ladies and Gentlemen:

     You have requested our opinion as to certain United States federal income
tax consequences of the merger (the "Merger") of Richfield State Agency, Inc., a
Minnesota corporation ("Seller"), with and into Marshall & Ilsley Corporation, a
Wisconsin corporation ("Company"). The Merger is being consummated pursuant to
the Agreement and Plan of Merger by and between Seller and Company dated as of
November 18, 2001 (the "Merger Agreement"). Unless otherwise defined,
capitalized terms used herein have the meanings assigned to them in the Merger
Agreement.

     In connection with rendering our opinion, we have reviewed the Merger
Agreement, including the Exhibits thereto, the Proxy Statement/Prospectus
constituting part of the Registration Statement on Form S-4 filed by Company
with the Securities and Exchange Commission on January 8, 2002, and such other
documents and corporate records as we have deemed necessary or appropriate as a
basis therefor. We have assumed that the representations and warranties
contained in the Merger Agreement were true, correct and complete when made and
will continue to be true, correct and complete through the Effective Time, and
that the parties have complied with and, if applicable, will continue to comply
with the covenants contained in the Merger Agreement. We also have assumed that
statements as to factual matters contained in the Proxy Statement/Prospectus are
true, correct, and complete and will continue to be true, correct, and complete
through the Effective Time. Finally, we have relied on the representations made
by officers of Seller and Company in tax certificates provided to us dated
January 7, 2002, and we have assumed that such representations will continue to
be true, correct, and complete through the Effective Time.




Richfield State Agency, Inc.
January 8, 2002
Page 2


     Based upon the foregoing, in reliance thereon and subject thereto, and
based upon the Internal Revenue Code of 1986, as amended (the "Code"), the
Treasury Regulations promulgated thereunder, judicial decisions, revenue rulings
and revenue procedures of the Internal Revenue Service, and other administrative
pronouncements, all as in effect on the date hereof, and assuming that the
Merger and related transactions will be consummated in accordance with the terms
of the Merger Agreement, it is our opinion that the Merger will qualify as a
reorganization within the meaning of Section 368(a) of the Code, and that each
of Seller and Company will be a party to such reorganization within the meaning
of Section 368(b) of the Code and accordingly, for United States federal income
tax purposes:

          (i)   No gain or loss will be recognized by Seller as a result of the
                Merger;

          (ii)  No gain or loss will be recognized by the shareholders of Seller
                who exchange their Seller Common Stock solely for Company Common
                Stock pursuant to the Merger (except with respect to cash
                received in lieu of a fractional share interest in Company
                Common Stock); and

          (iii) The aggregate tax basis of the Company Common Stock received by
                shareholders who exchange their Seller Common Stock solely for
                Company Common Stock pursuant to the Merger will be the same as
                the aggregate tax basis of the Seller Common Stock surrendered
                in exchange therefore (reduced by any amount allocable to a
                fractional share interest for which cash is received).

     No opinion is expressed as to any matter not specifically addressed above,
including the accuracy of the representations or reasonableness of the
assumptions relied upon by us in rendering the opinion set forth above. Our
opinion is based on current United States federal income tax law and
administrative practice, and we do not undertake to advise you as to any future
changes in United States federal income tax law or administrative practice that
may affect our opinion unless we are specifically retained to do so. We consent
to the use of this opinion as an Exhibit to the Registration Statement on Form
S-4 that includes the Proxy Statement/Prospectus, and to the references to
Fredrikson & Byron, P.A. under the captions "The Transaction--Material Federal
Income Tax Consequences" and "Legal Opinions" in the Proxy Statement/Prospectus.
In giving our consent, we do not admit that we are "experts" within the meaning
of Section 11 of the Securities Act of 1933 or within the category of persons
whose consent is required by Section 7 of the Securities Act of 1933.

                                                  Very truly yours,

                                                  /s/ Fredrikson & Byron, P.A.
                                                  FREDRIKSON & BYRON, P.A.





Richfield State Agency, Inc.
January 8, 2002
Page 3

                                                        FREDRIKSON & BYRON, P.A.