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EXHIBIT 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (Nos. 333-21241, No. 333-55126, 333-111314 and 333-125724) of Genzyme Corporation of our report dated June 27, 2005 relating to the financial statements of the Genzyme Corporation 401(k) Plan, which appears in this Form 11-K.

/s/ PricewaterhouseCoopers LLP

Boston, Massachusetts
June 27, 2005

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CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM