LETTER FROM PRICEWATERHOUSECOOPERS LLP
                                                                      EXHIBIT 16



December 19, 2001

Securities and Exchange Commission
450 Fifth Street, NW
Washington, D.C. 20549

Commissioners:

We have read the statements made by Exelixis, Inc. (copy attached), which we
understand will be filed with the Commission, pursuant to Item 4 of Form 8-K, as
part of the Company's Form 8-K report dated December 14, 2001. We agree with the
statements concerning our Firm in such Form 8-K.

Very truly yours,

/s/ PricewaterhouseCoopers LLP
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