Exhibit 99 Securities and Exchange Commission 450 Fifth Street, N.W. Washington, D.C. 20549 Re: Vertex Pharmaceuticals Incorporated Registration on Form S-8 We are aware that our report dated July 22, 1998 on our review of interim financial information of Vertex Pharmaceuticals Incorporated for the three month and six month periods ended June 30, 1998 and included in the Company's quarterly report on Form 10-Q for the quarter then ended is incorporated by reference in the Company's registration statements on Form S-8 (File Nos. 33-48030, 33-48348, 33-65742, 33-93224, 33-12325, 333-27011 and 333-56179). Pursuant to Rule 436(c) under the Securities Act of 1933, this report should not be considered a part of the registration statement prepared or certified by us within the meaning of Sections 7 and 11 of that Act. PricewaterhouseCoopers LLP Boston MA August 13, 1998