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EXHIBIT 31.a

CERTIFICATION OF CHIEF EXECUTIVE OFFICER
PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002.

I, Roger H. Ballou, certify that:



|1. |  | I have reviewed this quarterly report on Form 10-Q of CDI Corp.;                                                                                                                                                                                                                                          
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|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;
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|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 and cash flows of
the registrant as of, and for, the periods presented in this report;                   
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|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 report is being prepared;
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| | 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 on such
evaluation; and                                                                                           
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| | c) |  | Disclosed in this report any change in the registrants
internal control over financial reporting that occurred during the
registrants most recent 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 of internal control over financial reporting,
to the registrants auditors and the audit committee of the registrants
board of directors:
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| | a) |  | all significant deficiencies and material weaknesses in the
design or operation of internal control over financial reporting
which are reasonably likely to adversely affect the registrants
ability to record, process, summarize and report financial
information; and
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| | 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: August 13, 2003

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