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                                  Exhibit 31.a

                                  CERTIFICATION

I, Roger H. Ballou, certify that:

1.   I have reviewed this annual report on Form 10-K of CDI Corp.;

2.   Based on my knowledge, this annual 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 annual report;

3.   Based on my knowledge, the financial statements, and other financial
     information included in this annual report, fairly present in all material
     respects the financial condition, results of operations and cash flows of
     the registrant as of, and for, the periods presented in this annual report;

4.   The registrant's other certifying officer and I are responsible for
     establishing and maintaining disclosure controls and procedures (as defined
     in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:

          a)   designed such disclosure controls and procedures, or caused such
               disclosure controls and procedures to be designed under our
               supervision, 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 annual report is being prepared;

          b)   evaluated the effectiveness of the registrant's disclosure
               controls and procedures and presented in this report our
               conclusions about the effectiveness of the disclosure controls
               and procedures, as of the end of the period covered by this
               report based upon such evaluation; and

          c)   disclosed in this report any change in the registrant's internal
               control over financial reporting that occurred during the
               registrant's fourth fiscal quarter that has materially affected,
               or is reasonably likely to materially affect, the registrant's
               internal control over financial reporting; and

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

          a)   all significant deficiencies and material weaknesses in the
               design or operation of internal controls over financial reporting
               which are reasonably likely to adversely affect the registrant's
               ability to record, process, summarize and report financial
               information; and

          b)   any fraud, whether or not material, that involves management or
               other employees who have a significant role in the registrant's
               internal control over financial reporting.

Date: March 12, 2004

                                          By: /s/ Roger H. Ballou
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                                          ROGER H. BALLOU
                                          President and Chief Executive Officer