Exhibit 99.1

     CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

         I, Mark J. Plush, Vice President and Chief Financial Officer of
Keithley Instruments, Inc. (the "Company"), certify, pursuant to Section 906 of
the Sarbanes-Oxley Act of 2002, that:

         (1) The Annual Report on Form 11-K of the Company's Retirement Savings
         Trust and Plan for the period ended December 31, 2002 which this
         certification accompanies fully complies with the requirements of
         section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

         (2) The information contained in the Report fairly presents, in all
         material respects, the financial condition and results of operations of
         the Plan.

/s/ Mark J. Plush
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Mark J. Plush
Vice President and Chief Financial Officer of Keithley Instruments, Inc., and
Plan Administrator of the Keithley Instruments, Inc. Retirement Savings
Trust and Plan

June 26, 2003



         I, Philip R. Etsler, Vice President Human Resources of Keithley
Instruments, Inc. (the "Company"), certify, pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, that:

         (1) The Annual Report on Form 11-K of the Company's Retirement Savings
         Trust and Plan for the period ended December 31, 2002 which this
         certification accompanies fully complies with the requirements of
         section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

         (2) The information contained in the Report fairly presents, in all
         material respects, the financial condition and results of operations of
         the Plan.

/s/ Philip R. Etlser
-----------------------------------------------------
Philip R. Etsler

Vice President Human Resources of Keithley Instruments, Inc., and
Plan Administrator of the Keithley Instruments, Inc. Retirement Savings Trust
and Plan

June 26, 2003

A signed original of this written statement required by Section 906 has been
provided to Keithley Instruments, Inc. and will be retained by Keithley
Instruments, Inc. and furnished to the Securities and Exchange Commission or its
staff upon request.