EXHIBIT 12



MARSHALL & ILSLEY CORPORATION

Computation of Ratio of Earnings to Fixed Charges

($000s)



|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|-------------------------------------------------------------------------------------------------------------- |  | ------------------------ | --------- | - | ---- | - | --------- | ---- |  | - | --------- | - |  | ---- | --------- | - |  | - | --------- | -
|                                                                                                               |  | Years Ended December 31, |          
|                                                                                                               |  | 2004                     |           |   | 2003 |   |           | 2002 |  |   | 2001      |   |  | 2000 |          
|Earnings:                                                                                                      |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Earnings before income taxes, extraordinary items and cumulative effect of changes in accounting principles    |  | $                        | 944,966   |   |      | $ | 758,387   |      |  | $ | 718,592   |   |  | $    | 501,045   |   |  | $ | 470,350   |  
|                                                                                                               |  |                          |           |   |     
|Fixed charges, excluding interest on deposits                                                                  |  |                          | 281,244   |   |      |   | 267,379   |      |  |   | 301,518   |   |  |      | 321,059   |   |  |   | 321,812   |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Earnings including fixed charges but excluding interest on deposits                                            |  |                          | 1,226,210 |   |      |   | 1,025,766 |      |  |   | 1,020,110 |   |  |      | 822,104   |   |  |   | 792,162   |  
|                                                                                                               |  |                          |           |   |     
|Interest on deposits                                                                                           |  |                          | 276,102   |   |      |   | 228,216   |      |  |   | 283,385   |   |  |      | 566,899   |   |  |   | 772,016   |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Earnings including fixed charges and interest on deposits                                                      |  | $                        | 1,502,312 |   |      | $ | 1,253,982 |      |  | $ | 1,303,495 |   |  | $    | 1,389,003 |   |  | $ | 1,564,178 |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Fixed Charges:                                                                                                 |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Interest Expense:                                                                                              |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|                                                                                                               |  |                          |           |   |     
|Short-term borrowings                                                                                          |  | $                        | 61,256    |   |      | $ | 81,070    |      |  | $ | 150,310   |   |  | $    | 188,587   |   |  | $ | 224,187   |  
|                                                                                                               |  |                          |           |   |     
|Long-term borrowings                                                                                           |  |                          | 196,440   |   |      |   | 163,348   |      |  |   | 127,343   |   |  |      | 110,842   |   |  |   | 78,773    |  
|                                                                                                               |  |                          |           |   |     
|One-third of rental expense for all operating leases (the amount deemed representative of the interest factor) |  |                          | 23,548    |   |      |   | 22,961    |      |  |   | 23,865    |   |  |      | 21,630    |   |  |   | 18,852    |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Fixed charges excluding interest on deposits                                                                   |  |                          | 281,244   |   |      |   | 267,379   |      |  |   | 301,518   |   |  |      | 321,059   |   |  |   | 321,812   |  
|                                                                                                               |  |                          |           |   |     
|Interest on deposits                                                                                           |  |                          | 276,102   |   |      |   | 228,216   |      |  |   | 283,385   |   |  |      | 566,899   |   |  |   | 772,016   |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Fixed charges including interest on deposits                                                                   |  | $                        | 557,346   |   |      | $ | 495,595   |      |  | $ | 584,903   |   |  | $    | 887,958   |   |  | $ | 1,093,828 |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Ratio of Earnings to Fixed Charges:                                                                            |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|                                                                                                               |  |                          |           |   |     
|Excluding interest on deposits                                                                                 |  |                          | 4.36      | x |      |   | 3.84      | x    |  |   | 3.38      | x |  |      | 2.56      | x |  |   | 2.46      | x
|                                                                                                               |  |                          |           |   |     
|Including interest on deposits                                                                                 |  |                          | 2.70      | x |      |   | 2.53      | x    |  |   | 2.23      | x |  |      | 1.56      | x |  |   | 1.43      | x