Exhibit 32.1

                       Certification Pursuant to 18 U.S.C.
                        Section 1350, As Adopted Pursuant
                      To Section 906 of the Sarbanes-Oxley
                                   Act of 2002

      In  connection  with the Quarterly  Report of Castelle (the  "Company") on
Form 10-Q/A for the period  ended March 31, 2004,  as filed with the  Securities
and Exchange Commission on the date hereof (the "Report"), I, Scott C. McDonald,
Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. ss. 1350,
as adopted  pursuant to ss. 906 of the  Sarbanes-Oxley  Act of 2002,  that to my
knowledge:

      (1)   The Report fully complies with the  requirements of Section 13(a) 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 Company.


              /s/ Scott C. McDonald
      Name:   Scott C. McDonald
      Title:  Chief Executive Officer

      Date:   May 4, 2005

This  certification  accompanies  this  report  pursuant  to Section  906 of the
Sarbanes-Oxley  Act of 2002 and shall not be deemed to be filed by Castelle  for
purposes of Section 18 of the Securities Exchange Act of 1934. A signed original
of this written statement  required by Section 906 has been provided to Castelle
and will be retained by Castelle and  furnished to the  Securities  and Exchange
Commission or its staff upon request.


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