Press Release

Whitehouse Station, NJ and Cambridge, MA, January 6, 2005 -- Merck & Co., Inc. (NYSE: MRK) and Vertex Pharmaceuticals Incorporated (Nasdaq: VRTX) announced today that they have begun a Phase I clinical study for VX-680, a small molecule inhibitor of Aurora kinases, in patients with solid tumor cancers. The open-label, dose escalation study conducted at two major cancer treatment centers is designed to evaluate the safety and tolerability of VX-680 when administered in multiple cycles to patients with solid tumors refractory to prior chemotherapy treatment. The initiation of this clinical study is supported by VX-680's activity in both in vitro and in vivo cancer models. Merck and Vertex plan to initiate additional Phase I studies of VX-680 this year.

Aurora kinases are implicated in the onset of many human cancers, and Aurora kinase inhibitors such as VX-680 have the potential to play an important role in the treatment and management of a wide range of tumor types. In June 2004, Vertex and Merck entered into a global collaboration to develop and commercialize VX-680. Along with clinical development, Vertex and Merck are conducting a joint research program to characterize VX-680's activity across a broad range of cancer types and will seek to identify additional drug candidates targeting the Aurora kinases.

"The Aurora kinases represent a target of high interest for the development of novel anti-cancer drugs because of the multiple roles Aurora kinases play in the development and progression of tumors," said Stephen H. Friend, M.D., Ph.D., Senior Vice President for Molecular Profiling and Cancer Research at Merck Research Laboratories. "Oncology represents a key area of focus for Merck, and compounds such as VX-680 could potentially create a foundation for new types of chemotherapy regimens in the future treatment of cancer."

Aurora Kinases and Cancer
Cancer cells typically contain mutations in a number of genes, which ultimately result in uncontrolled cell growth and tumor metastasis. As enzymes specific for and essential to cell growth and division, Aurora kinases hold the potential to be important control points for slowing the growth and spread of tumors. Aurora kinases (also known as BTAK and STK15) are a family of serine-threonine kinases that are believed to play multiple roles in the development and progression of cancer, by acting as regulators of cell proliferation, by transforming normal cells into cancer cells and by down-regulating p53, one of the body's natural tumor suppressors. Aurora kinases are known to be over-expressed in many tumor types, including colon cancer, breast cancer and leukemia. Amplification of Aurora genes is associated with progression of colorectal cancer and poor prognosis in certain types of breast cancer.

Discovery of VX-680
VX-680 was discovered by scientists at Vertex's Oxford, U.K. research site as part of a broad research effort targeting the kinase gene family. Vertex researchers published the three-dimensional atomic crystal structure of Aurora-A kinase in 2002, a key scientific advance that enabled the design and optimization of multiple classes of small molecule Aurora kinase inhibitors. VX-680 was advanced to preclinical development in 2002, following evaluation of the compound's activity in tumor cell lines and in animal models of tumor growth. In studies published early in 2004, Vertex demonstrated that VX-680 induced tumor regression in xenograft models of human pancreatic and colon cancer. In addition, Vertex has presented data that shows that VX-680 prolonged survival and induced sustained remission in an oncogene driven model of human acute myelocytic leukemia (AML).

About Merck
Merck & Co., Inc. is a global research-driven pharmaceutical company dedicated to putting patients first. Established in 1891, Merck discovers, develops, manufactures and markets vaccines and medicines in more than 20 therapeutic categories. The company also devotes extensive efforts to increase access to medicines through far-reaching programs that not only donate Merck medicines but help deliver them to the people who need them. Merck also publishes unbiased health information as a not-for-profit service. For more information, visit www.merck.com.

About Vertex
Vertex Pharmaceuticals Incorporated is a global biotechnology company committed to the discovery and development of breakthrough small molecule drugs for serious diseases. The Company's strategy is to commercialize its products both independently and in collaboration with major pharmaceutical partners. Vertex's product pipeline is principally focused on viral diseases, inflammation, autoimmune diseases and cancer. Vertex co-promotes the HIV protease inhibitor, Lexiva(R), with GlaxoSmithKline. Lexiva(R) is a registered trademark of the GlaxoSmithKline group of companies.

Lexiva(R) is a registered trademark of the GlaxoSmithKline group of companies.

Merck Forward-Looking Statement
This press release contains "forward-looking statements" as that term is defined in the Private Securities Litigation Reform Act of 1995. These statements involve risks and uncertainties, which may cause results to differ materially from those set forth in the statements. The forward-looking statements may include statements regarding product development, product potential or financial performance. No forward-looking statement can be guaranteed, and actual results may differ materially from those projected. Merck undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events, or otherwise. Forward-looking statements in this press release should be evaluated together with the many uncertainties that affect Merck's business, particularly those mentioned in the cautionary statements in Item 1 of Merck's Form 10-K for the year ended Dec. 31, 2003, and in its periodic reports on Form 10-Q and Form 8-K, which the company incorporates by reference.

Vertex Forward-Looking Statement
This press release may contain forward-looking statements, including statements that (i) Merck and Vertex plan to initiate additional Phase I studies of VX-680 this year; (ii) compounds such as VX-680 have the potential to play an important role in the treatment and management of a wide range of tumor types, and could create a foundation for new types of chemotherapeutic regimens; (iii) Vertex and Merck are conducting a joint research program to characterize VX-680's activity across a broad range of cancer types, and will seek to identify additional drug candidates targeting the Aurora kinases. While management makes its best efforts to be accurate in making forward-looking statements, such statements are subject to risks and uncertainties that could cause the actual results of studies to vary materially. Those risks and uncertainties include the risk that non-clinical results targeting Aurora kinases may not be predictive of human clinical results in the treatment of cancer, that development of VX-680 may not be pursued due to clinical, technical or financial issues, that the rate of patient enrollment may limit expected study timelines and follow-on studies, that Merck may choose to not develop VX-680 or any other Aurora kinase inhibitor discovered by Vertex for commercial or scientific reasons, and other risks listed under Risk Factors in Vertex's Form 10-K filed with the Securities and Exchange Commission on March 15, 2004 and amended on September 8, 2004.

Vertex Contacts:
Lynne H. Brum, VP, Corporate Communications and Financial Planning, (617) 444-6614
Michael Partridge, Director, Corporate Communications, (617) 444-6108
Zachry Barber, Specialist, Media Relations, (617) 444-6470

Merck Contacts:
Media Relations: Janet Skidmore, (908) 423-3046
Investor Relations: Michael Rabinowitz, (908) 423-5185