<PAGE>

                                                                   EXHIBIT 99.26



                     MONTHLY CERTIFICATEHOLDERS' STATEMENT

                             FIRST USA BANK, N.A.

              ---------------------------------------------------
               FIRST USA CREDIT CARD MASTER TRUST, SERIES 1998-6
              ---------------------------------------------------

                Monthly Period:                  3/1/00 to
                                                 3/31/00
                Distribution Date:               4/18/00
                Transfer Date:                   4/17/00

Under Section 5.02 of the Pooling and Servicing Agreement dated as of
September 1, 1992 (the "Pooling and Servicing Agreement") by and between First
USA Bank, N.A. (the "Bank") and The Bank of New York (Delaware), as trustee (the
"Trustee") the Bank, as Servicer, is required to prepare certain information
each month regarding current distributions to Certificateholders and the
performance of the First USA Credit Card Master Trust (the "Trust") during the
previous month. The information which is required to be prepared with respect to
the Distribution Date noted above and with respect to the performance of the
Trust during the month noted above is set forth below. Certain information is
presented on the basis of an original principal amount of $1,000 per Series
1998-6 Certificate (a "Certificate"). Certain other information is presented
based on the aggregate amount for the Trust as a whole. Capitalized terms used
in this Monthly Certificateholders' Statement have their respective meanings set
forth in the Pooling and Servicing Agreement.

A.  Information Regarding the Current Monthly Distribution.
    -------------------------------------------------------

    1.  The total amount of the distribution to
        Certificateholders on the Distribution Date per
        $1,000 original certificate principal amount
                              Class A                               $5.01962
                              Class B                               $5.18073
                              Excess Collateral Amount              $5.13333

    2.  The amount of the distribution set forth
        in paragraph 1 above in respect of
        interest on the Certificates, per $1,000
        original certificate principal amount
                              Class A                               $5.01962
                              Class B                               $5.18073
                              Excess Collateral Amount              $5.13333

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MONTHLY CERTIFICATEHOLDERS' STATEMENT                             Series 1998-6
Page 2


    3.  The amount of the distribution set forth
        in paragraph 1 above in respect of
        principal on the Certificates, per $1,000
        original certificate principal amount
                              Class A                                  $0.00000
                              Class B                                  $0.00000
                              Excess Collateral Amount                 $0.00000

B.  Information Regarding the Performance of the Trust.
    ---------------------------------------------------

    1.  Allocation of Principal Receivables.
        ------------------------------------

        The aggregate amount of Allocations of
        Principal Receivables processed during the
        Monthly Period which were allocated in
        respect of the Certificates
                              Class A                           $124,487,010.42
                              Class B                            $11,228,014.34
                              Excess Collateral Amount           $14,222,151.54
                                                          ---------------------
                              Total                             $149,937,176.30

    2.  Allocation of Finance Charge Receivables
        ----------------------------------------

        (a1)  The aggregate amount of Allocations of
              Finance Charge Receivables processed
              during the Monthly Period which were
              allocated in respect of the Certificates
                              Class A                            $12,476,260.74
                              Class B                             $1,125,287.16
                              Excess Collateral Amount            $1,425,363.73
                                                          ---------------------
                              Total                              $15,026,911.63

        (b1)  Principal Funding Investment Proceeds
              (to Class A)                                                $0.00
        (b2)  Withdrawals from Reserve Account
              (to Class A)                                                $0.00
                                                          ---------------------
              Class A Available Funds                            $12,476,260.74

        (c1)  Principal Funding Investment Proceeds
              (to Class B)                                                $0.00
        (c2)  Withdrawals from Reserve Account
              (to Class B)                                                $0.00
              Class B Available Funds                              1,125,287.16

        (d1)  Prin. Funding Investment Proceeds
              (to CIA)                                                    $0.00
        (d2)  Withdrawals from Reserve Account
              (to CIA)                                                    $0.00
              CIA Available Funds                                  1,425,363.73

        (e1)  Total Principal Funding Investment Proceeds                  0.00
        (e2)  Investment Earnings on deposits to Reserve Account          $0.00

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MONTHLY CERTIFICATEHOLDERS' STATEMENT                             Series 1998-6
Page 3


    3.  Principal Receivable/Investor Percentages
        -----------------------------------------

        (a)   The aggregate amount of Principal
              Receivables in the Trust as of the
              last day of the Monthly Period                 $36,401,753,059.56

        (b)   Invested Amount as of the last day of
              the preceding month (Adjusted Class A
              Invested Amount during Accumulation
              Period)
                              Class A                           $800,000,000.00
                              Class B                            $72,289,000.00
                              Excess Collateral Amount           $91,567,000.00
                                                          ---------------------
                              Total                             $963,856,000.00

        (c)   The Floating Allocation Percentage:
              The Invested Amount set forth in paragraph
              3(b) above as a percentage of the aggregate
              amount of Principal Receivables as of the
              Record Date set forth in paragraph 3(a) above
                              Class A                                     2.198%
                              Class B                                     0.199%
                              Excess Collateral Amount                    0.252%
                                                                          ------
                              Total                                       2.649%

        (d)   During the Amortization Period: The
              Invested Amount as of __________ (the
              last day of the Revolving Period)
                              Class A                                     $0.00
                              Class B                                     $0.00
                              Excess Collateral Amount                    $0.00
                                                          ---------------------
                              Total                                       $0.00

        (e)   The Fixed/Floating Allocation Percentage:
              The Invested Amount set forth in paragraph
              3(d) above as a percentage of the aggregate
              amount of Principal Receivables set forth
              in paragraph 3(a) above
                              Class A                                     0.000%
                              Class B                                     0.000%
                              Excess Collateral Amount                    0.000%
                                                                          ------
                              Total                                       0.000%

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MONTHLY CERTIFICATEHOLDERS' STATEMENT                             Series 1998-6
Page 4


    4.  Delinquent Balances.
        --------------------

        The aggregate amount of outstanding balances
        in the Accounts which were delinquent as of
        the end of the day on the last day of the
        Monthly Period

        (a)   35 - 64 days                                      $429,919,820.18
        (b)   65 - 94 days                                      $308,515,296.32
        (c)   95 - 124 days                                     $259,370,109.95
        (d)   125 - 154 days                                    $229,194,360.22
        (e)   155 - 184 days                                    $213,948,592.85
        (f)   185 or more days                                            $0.00
                                                                          -----
                              Total                           $1,440,948,179.52

    5.  Monthly Investor Default Amount.
        --------------------------------

        (a)   The aggregate amount of all defaulted
              Principal Receivables written off as
              uncollectible during the Monthly Period
              allocable to the Invested Amount (the
              aggregate "Investor Default Amount")
                              Class A                             $3,278,541.53
                              Class B                               $295,705.64
                              Excess Collateral Amount              $374,560.48
                                                                    -----------
                              Total                               $3,948,807.65

    6.  Investor Charge-Offs & Reimbursements of Charge-Offs.
        -----------------------------------------------------

        (a)   The aggregate amount of Class A Investor
              Charge-Offs and the reductions in the
              Class B Invested Amount and the Excess
              Collateral Amount
                              Class A                                     $0.00
                              Class B                                     $0.00
                              Excess Collateral Amount                    $0.00
                                                          ---------------------
                              Total                                       $0.00

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MONTHLY CERTIFICATEHOLDERS' STATEMENT                             Series 1998-6
Page 5


        (b)   The aggregate amount of Class A Investor
              Charge-Offs reimbursed and the reimbursement
              of reductions in the Class B Invested Amount
              and the Excess Collateral Amount

                              Class A                                     $0.00
                              Class B                                     $0.00
                              Excess Collateral Amount                    $0.00
                                                          ---------------------
                              Total                                       $0.00

    7.  Investor Servicing Fee
        ----------------------
        (a)   The amount of the Investor Monthly
              Servicing Fee payable by the Trust
              to the Servicer for the Monthly
              Period

                              Class A                             $1,000,000.00
                              Class B                                $90,361.25
                              Excess Collateral Amount              $114,458.75
                                                                    -----------
                              Total                               $1,204,820.00

    8.  Reallocated Principal Collections
        ---------------------------------
              The amount of Reallocated Excess Collateral
              and Class B Principal Collections applied
              in respect of Interest Shortfalls, Investor
              Default Amounts or Investor Charge-Offs for
              the prior month.

                              Class B                                     $0.00
                              Excess Collateral Amount                    $0.00
                                                                          -----
                              Total                                       $0.00

    9.  Excess Collateral Amount
        (a)   The amount of the Excess Collateral
              Amount as of the close of business
              on the related Distribution Date after
              giving effect to withdrawals, deposits and
              payments to be made in respect of the
              preceding month                                    $91,567,000.00

    10. The Portfolio Yield
        -------------------
           The Portfolio Yield for the related Monthly Period             13.79%

    11. The Base Rate
        -------------
           The Base Rate for the related Monthly Period                    8.24%

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MONTHLY CERTIFICATEHOLDERS' STATEMENT                             Series 1998-6
Page 6


C   Information Regarding the Principal Funding Account
    ---------------------------------------------------

        1.    Accumulation Period

        (a)   Accumulation Period commencement date                  12/01/2007

        (b)   Accumulation Period Length (months)                         8

        (c)   Accumulation Period Factor                               1.00

        (d)   Required Accumulation Factor Number                         8

        (e)   Controlled Accumulation Amount                $120,482,000.00

        (f)   Minimum Payment Rate (last 12 months)                  14.06%

        2.  Principal Funding Account
            -------------------------

            Beginning Balance                                             $0.00
                Plus: Principal Collections for Related
                      Monthly Period from Principal Account               $0.00
                Plus: Interest on Principal Funding Account
                      Balance for Related Monthly Period                  $0.00

                Less: Withdrawals to Finance Charge Account               $0.00
                Less: Withdrawals to Distribution Account                 $0.00
                                                              -----------------
            Ending Balance                                                $0.00

        3.  Accumulation Shortfall
            ----------------------

                  The Controlled Deposit Amount for
                  the previous Monthly Period                             $0.00

            Less: The amount deposited into the
                  Principal Funding Account for the
                  Previous Monthly Period                                 $0.00

                  Accumulation Shortfall                                  $0.00
                                                              -----------------
                  Aggregate Accumulation Shortfalls                       $0.00

        4.  Principal Funding Investment Shortfall
            --------------------------------------

                  Covered Amount                                          $0.00

            Less: Principal Funding Investment Proceeds                   $0.00
                                                             ------------------
                  Principal Funding Investment Shortfall                  $0.00
                                                             ------------------


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MONTHLY CERTIFICATEHOLDERS' STATEMENT                             Series 1998-6
Page 7


D.  Information Regarding the Reserve Account
    -----------------------------------------

       1.  Required Reserve Account Analysis
           ---------------------------------

           (a)   Required Reserve Account Amount                        0.00000%

           (b)   Required Reserve Account Amount ($)
                 (0.5% of Invested Amount or other
                 amount designated by Transferor)                         $0.00

           (c)   Required Reserve Account Balance after
                 effect of any transfers on the Related
                 Transfer Date                                            $0.00

           (d)   Reserve Draw Amount transferred to the
                 Finance Charge Account on the Related
                 Transfer Date                                            $0.00

       2.  Reserve Account Investment Proceeds
           -----------------------------------
           Reserve Account Investment Proceeds transferred
           to the Finance Charge Account on the Related
           Transfer Date                                                  $0.00

       3.  Withdrawals from the Reserve Account
           ------------------------------------
           Total Withdrawals from the Reserve Account
           transferred to the Finance Charge Account on
           the related Transfer Date (1(d) plus 2 above)                   0.00

       4.  The Portfolio Adjusted Yield
           ----------------------------
           The Portfolio Adjusted Yield for the related
           Monthly Period                                                  4.88%

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MONTHLY CERTIFICATEHOLDERS' STATEMENT
Signature Page





                                 First USA Bank, N.A.
                                 as Servicer


                                 By:  /s/ Tracie Klein
                                     -------------------------------------
                                     Tracie Klein
                                     First Vice President