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FORM N-CSR ITEM 10(c) EXHIBIT


                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

          The undersigned hereby certify in their capacity as Treasurer and
President, respectively, of Tax-Managed Mid-Cap Core Portfolio (the
"Portfolio"), that:

     (a)  the Semi-Annual Report of the Portfolio on Form N-CSR for the period
          ended April 30, 2003 (the "Report") fully complies with the
          requirements of Section 13(a) or 15(d) of the Securities Exchange Act
          of 1934, as amended; and

     (b)  the information contained in the Report fairly presents, in all
          material respects, the financial condition and the results of
          operations of the Portfolio for such period.

A SIGNED ORIGINAL OF THIS WRITTEN STATEMENT REQUIRED BY SECTION 906 HAS BEEN
PROVIDED TO THE PORTFOLIO AND WILL BE RETAINED BY THE PORTFOLIO AND FURNISHED TO
THE SECURITIES AND EXCHANGE COMMISSION OR ITS STAFF UPON REQUEST.

Date: June 18, 2003

/s/ Michelle A. Alexander
- ----------------------------------
Michelle A. Alexander
Treasurer

Date: June 18, 2003
      ----------------------------

/s/ James B. Hawkes
- ----------------------------------
James B. Hawkes
President