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FORM N-CSR ITEM 10(a) EXHIBIT

Not Applicable

FORM N-CSR ITEM 10(b) EXHIBIT

I, Michelle A. Alexander; certify that:

1. I have reviewed this report on Form N-CSR of Tax-Managed Mid-Cap Core
Portfolio;

2. Based on my knowledge, this report does not contain any untrue statement of a
material fact or omit to state a material fact necessary to make the statements
made, in light of the circumstances under which such statements were made, not
misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial
information included in this report, fairly present in all material respects the
financial condition, results of operations, changes in net assets, and cash
flows (if the financial statements are required to include a statement of cash
flows) of the registrant as of, and for, the periods presented in this report;

4. The registrant's other certifying officers and I are responsible for
establishing and maintaining disclosure controls and procedures (as defined in
rule 30a-2(c) under the Investment Company Act of 1940) for the registrant and
have:

a) designed such disclosure controls and procedures to ensure that material
information relating to the registrant, including its consolidated subsidiaries,
is made known to us by others within those entities, particularly during the
period in which this report is being prepared;

b) evaluated the effectiveness of the registrant's disclosure controls and
procedures as of a date within 90 days prior to the filing date of this report
(the "Evaluation Date"); and

c) presented in this report our conclusions about the effectiveness of the
disclosure controls and procedures based on our evaluation as of the Evaluation
Date;

5. The registrant's other certifying officers and I have disclosed, based on our
most recent evaluation, to the registrant's auditors and the audit committee of
the registrant's board of directors (or persons performing the equivalent
functions):

a) all significant deficiencies in the design or operation of the internal
controls which could adversely affect the registrant's ability to record,
process, summarize, and report financial data and have identified for the
registrant's auditors any material weaknesses in internal controls; and

b) any fraud, whether or not material, that involves management or other
employees who have a significant role in the registrant's internal controls; and
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6. The registrant's other certifying officers and I have indicated in this
report whether or not there were significant changes in internal controls or in
other factors that could significantly affect internal controls subsequent to
the date of our most recent evaluation, including any corrective actions with
regard to significant deficiencies and material weaknesses.


Date:    June 18, 2003

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



I, James B. Hawkes; certify that:

1. I have reviewed this report on Form N-CSR of Tax-Managed Mid-Cap Core
Portfolio;

2. Based on my knowledge, this report does not contain any untrue statement of a
material fact or omit to state a material fact necessary to make the statements
made, in light of the circumstances under which such statements were made, not
misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial
information included in this report, fairly present in all material respects the
financial condition, results of operations, changes in net assets, and cash
flows (if the financial statements are required to include a statement of cash
flows) of the registrant as of, and for, the periods presented in this report;

4. The registrant's other certifying officers and I are responsible for
establishing and maintaining disclosure controls and procedures (as defined in
rule 30a-2(c) under the Investment Company Act of 1940) for the registrant and
have:

a) designed such disclosure controls and procedures to ensure that material
information relating to the registrant, including its consolidated subsidiaries,
is made known to us by others within those entities, particularly during the
period in which this report is being prepared;

b) evaluated the effectiveness of the registrant's disclosure controls and
procedures as of a date within 90 days prior to the filing date of this report
(the "Evaluation Date"); and

c) presented in this report our conclusions about the effectiveness of the
disclosure controls and procedures based on our evaluation as of the Evaluation
Date;
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5. The registrant's other certifying officers and I have disclosed, based on our
most recent evaluation, to the registrant's auditors and the audit committee of
the registrant's board of directors (or persons performing the equivalent
functions):

a) all significant deficiencies in the design or operation of the internal
controls which could adversely affect the registrant's ability to record,
process, summarize, and report financial data and have identified for the
registrant's auditors any material weaknesses in internal controls; and

b) any fraud, whether or not material, that involves management or other
employees who have a significant role in the registrant's internal controls; and

6. The registrant's other certifying officers and I have indicated in this
report whether or not there were significant changes in internal controls or in
other factors that could significantly affect internal controls subsequent to
the date of our most recent evaluation, including any corrective actions with
regard to significant deficiencies and material weaknesses.


Date:    June 18, 2003

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