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                                                           Exhibit 31(a)
                              CERTIFICATION
                              _____________

I, Dennis J. Kuester, President and Chief Executive Officer of Marshall &
Ilsley Corporation, certify that:

     1.   I have reviewed this quarterly report on Form 10-Q of Marshall
          & Ilsley Corporation;

     2.   Based on my knowledge, this report does not contain any untrue
          statement of a material fact or omit to state a material fact
          necessary to make the statements made, in light of the
          circumstances under which such statements were made, not
          misleading with respect to the period covered by this report;

     3.   Based on my knowledge, the financial statements, and other
          financial information included in this report, fairly present
          in all material respects the financial condition, results of
          operations and cash flows of the registrant as of, and for, the
          periods presented in this report;

     4.   The registrant's other certifying officer(s) and I are
          responsible for establishing and maintaining disclosure controls
          and procedures (as defined in Exchange Act Rules 13a-15(e) and
          15d-15(e)) for the registrant and have:

          (a)  Designed such disclosure controls and procedures, or
               caused such disclosure controls and procedures to be
               designed under our supervision, to ensure that material
               information relating to the registrant, including its
               consolidated subsidiaries, is made known to us by others
               within those entities, particularly during the period in
               which this report is being prepared;

          (b)  Evaluated the effectiveness of the registrant's
               disclosure controls and procedures and presented in this
               report our conclusions about the effectiveness of the
               disclosure controls and procedures, as of the end of the
               period covered by this report based on such evaluation;
               and

          (c)  Disclosed in this report any change in the registrant's
               internal control over financial reporting that occurred
               during the registrant's most recent fiscal quarter (the
               registrant's fourth fiscal quarter in the case of an
               annual report) that has materially affected, or is
               reasonably likely to materially affect, the registrant's
               internal control over financial reporting; and

     5.   The registrant's other certifying officer(s) and I have
          disclosed, based on our most recent evaluation of internal
          control over financial reporting, to the registrant's auditors
          and the audit committee of the registrant's board of directors
          (or persons performing the equivalent functions):

          (a)  All significant deficiencies and material weaknesses in
               the design or operation of internal control over
               financial reporting which are reasonably likely to
               adversely affect the registrant's ability to record,
               process, summarize and report financial information; and

          (b)  Any fraud, whether or not material, that involves
               management or other employees who have a significant role
               in the registrant's internal control over financial
               reporting.

Dated:  November 9, 2004

/s/ Dennis J. Kuester
_____________________________________

Dennis J. Kuester
President and Chief Executive Officer


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