EXHIBIT 99.1
CERTIFICATION

Pursuant to Section 906 of the Public Company Accounting Reform and Investor
Protection Act of 2002 (18 U.S.C. Section 1350, as adopted) (the Sarbanes-Oxley
Act of 2002), Joseph D. Keegan, Ph.D., the Chief Executive Officer of Molecular
Devices Corporation (the "Company"), and Timothy A. Harkness, the Chief
Financial Officer of the Company, each hereby certifies that, to his knowledge:

1. The Company's Quarterly Report on Form 10-Q/A for the period ended March 31,
2003, to which this Certification is attached as Exhibit 99.1 (the "Periodic
Report"), fully complies with the requirements of Section 13(a) or Section 15(d)
of the Securities Exchange Act of 1934, as amended; and

2. The information contained in the Periodic Report fairly presents, in all
material respects, the financial condition of the Company at the end of the
periods covered by the Periodic Report and results of operations of the Company
for the periods covered by the Periodic Report.

This certification accompanies the Periodic Report pursuant to Section 906 of
the Sarbanes-Oxley Act of 2002 and shall not be deemed "filed" by the Company
for purposes of Section 18 of the Securities Exchange Act of 1934, as amended.

Dated: May 16, 2003


/s/ JOSEPH D. KEEGAN                            /s/ TIMOTHY A. HARKNESS
- ---------------------------                     ---------------------------
Joseph D. Keegan, Ph.D.                         Timothy A. Harkness
Chief Executive Officer                         Chief Financial Officer


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