Exhibit 12
                           MARSHALL & ILSLEY CORPORATION
                  COMPUTATION OF RATIO OF EARNINGS TO FIXED CHARGES
                                    ($000's)


                                                       Three
                                                       Months
                                                       Ended                         Years Ended December 31,
                                                      March 31,  ----------------------------------------------------------------
                                                        2003          2002         2001         2000         1999         1998
                                                    ------------ ------------ ------------ ------------ ------------ ------------
                                                                                                 
Earnings:
  Earnings before income taxes, extraordinary
   items and cumulative effect of changes
    in accounting principles                       $    193,634 $    718,592 $    501,045 $    470,350 $    527,939 $    465,285

  Fixed charges, excluding interest on deposits          70,243      301,518      321,059      321,812      222,172      206,546
                                                     -----------  -----------  -----------  -----------  -----------  -----------
       Earnings including fixed charges but
         excluding interest on deposits                 263,877    1,020,110      822,104      792,162      750,111      671,831

  Interest on deposits                                   62,827      283,385      566,899      772,016      585,864      564,540
                                                     -----------  -----------  -----------  -----------  -----------  -----------
       Earnings including fixed charges and
         interest on deposits                      $    326,704 $  1,303,495 $  1,389,003 $  1,564,178 $  1,335,975 $  1,236,371
                                                     ===========  ===========  ===========  ===========  ===========  ===========
Fixed Charges:

  Interest Expense:

     Short-term borrowings                         $     22,050 $    150,310 $    188,587 $    224,187 $    142,294 $    126,624

     Long-term borrowings                                42,227      127,343      110,842       78,773       63,145       66,810

     One-third of rental expense for all operating
       leases (the amount deemed representative
       of the interest factor)                            5,966       23,865       21,630       18,852       16,733       13,112
                                                     -----------  -----------  -----------  -----------  -----------  -----------
     Fixed charges excluding interest on deposits        70,243      301,518      321,059      321,812      222,172      206,546

     Interest on deposits                                62,827      283,385      566,899      772,016      585,864      564,540
                                                     -----------  -----------  -----------  -----------  -----------  -----------
     Fixed charges including interest on deposits  $    133,070 $    584,903 $    887,958 $  1,093,828 $    808,036 $    771,086
                                                     ===========  ===========  ===========  ===========  ===========  ===========
Ratio of Earnings to Fixed Charges:

  Excluding interest on deposits                           3.76 x       3.38 x       2.56 x       2.46 x       3.38 x       3.25 x

  Including interest on deposits                           2.46 x       2.23 x       1.56 x       1.43 x       1.65 x       1.60 x