[Arthur Andersen LLP Letterhead]                                   Exhibit 99(a)


February 23, 2001

Office of the Chief Accountant
Securities and Exchange Commission
450 Fifth Street, NW
Washington, D.C. 20549

Dear Sir/Madam:

We have read the relevant information referring to our firm in Item 4 included
in the Form 8-K dated February 23, 2001, of BANK ONE CORPORATION filed with the
Securities and Exchange Commission and are in agreement with the statements
contained therein.

Very truly yours,

/s/ Arthur Andersen LLP

Arthur Andersen LLP


cc:   Charles W. Scharf
        Chief Financial Officer,
        BANK ONE CORPORATION

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