Exhibit 23

Consent of Independent Registered Public Accounting Firm

We hereby consent to the incorporation by reference in the Registration Statement on Forms S-8 (Nos. 33-21087, 33-21088, 33-40177, 33-51235, 33-53463, 33-64273, 33-64665, 333-91769, 333-30526, 333-31762, 333-40282, 333-53246, 333-56696, 333-72206, 333-65796, 333-101519 and 333-109296) of Merck & Co., Inc. of our report dated June 17, 2005 relating to the financial statements of Merck Puerto Rico Employee Savings and Security Plan as of December 31, 2004 and 2003 and for the year ended December 31, 2004, which appears in this Form 11-K.

/s/PricewaterhouseCoopers LLP

San Juan, Puerto Rico
June 27, 2005

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