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                                                                     EXHIBIT 5.1

                                HALE AND DORR LLP
                               Counsellors At Law
                  60 State Street, Boston, Massachusetts 02451
                         617-526-6000 * FAX 617-526-5000


                                           May 16, 2000


PAREXEL International Corporation
195 West Street
Waltham, MA  02451

         Re:      2000 Employee Stock Purchase Plan
                  ---------------------------------

Ladies and Gentlemen:

We have assisted in the preparation of a Registration Statement on Form S-8 (the
"Registration Statement") to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, as amended (the "Securities Act"),
relating to an aggregate of 800,000 shares of Common Stock, $.01 par value per
share (the "Shares"), of PAREXEL International Corporation, a Massachusetts
corporation (the "Company"), issuable under the Company's 2000 Employee Stock
Purchase Plan (the "Plan").

We have examined the Articles of Organization and By-Laws of the Company, each
as amended and restated to date and originals, or copies certified to our
satisfaction, of all pertinent records of the meetings of the directors and
stockholders of the Company, the Registration Statement and such other documents
relating to the Company as we have deemed material for the purposes of this
opinion.

In our examination of the foregoing documents, we have assumed the genuineness
of all signatures, the authenticity of all documents submitted to us as
originals, the conformity to original documents of all documents submitted to us
as copies, the authenticity of the originals of such latter documents and the
legal competence of all signatories to such documents.

We assume that the appropriate action will be taken, prior to the offer and sale
of the Shares in accordance with the Plan, to register and qualify the Shares
for sale under all applicable state securities or "blue sky" laws.

We express no opinion herein as to the laws of any state or jurisdiction other
than the state laws of the Commonwealth of Massachusetts and the federal laws of
the United States of America.



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Based upon and subject to the foregoing, we are of the opinion that the Shares
have been duly authorized for issuance and, when the Shares are issued and paid
for in accordance with the terms and conditions of the Plan, the Shares will be
validly issued, fully paid and nonassessable.

It is understood that this opinion is to be used only in connection with the
offer and sale of the Shares while the Registration Statement is in effect.

Please note that we are opining only as to the matters expressly set forth
herein, and no opinion should be inferred as to any other matters.

We hereby consent to the filing of this opinion with the Commission as an
exhibit to the Registration Statement in accordance with the requirements of
Item 601(b)(5) of Regulation S-K under the Securities Act. In giving such
consent, we do not hereby admit that we are in the category of persons whose
consent is required under Section 7 of the Securities Act or the rules and
regulations of the Commission.

                                             Very truly yours,

                                             /s/ Hale and Dorr LLP

                                             HALE AND DORR LLP






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