January 6. 2004

FOR IMMEDIATE RELEASE

Dr. George M. Milne, Jr. Joins Rib-X Pharmaceuticals Board Of Directors

Former Pfizer Executive also to Serve as Consultant to this Antibiotic Development Company

NEW HAVEN, Conn., Jan. 6 /PRNewswire/ -- Rib-X Pharmaceuticals, Inc., a privately held biotechnology company developing the next generation of antibiotics, announced today that George M. Milne, Jr., Ph.D., a former Executive Vice President for Global Research and Development at Pfizer Inc., has joined its Board of Directors. Dr. Milne will also serve as a consultant to Rib-X. This appointment brings the number of board members to eight.

"There is a critical need globally for new classes of antibiotics," said Dr. George M. Milne Jr. "Rib-X has combined a world class antibiotics research and development team with exciting state of the art structure based design technology that is focused on overcoming drug resistant bacterial infections. This combination has enabled the Company to attract exceptional financial support from the venture capital community. Collectively, these resources provide the Company a strong opportunity to bring a succession of new anti-infective drugs into the marketplace."

Dr. Milne's thirty-two year career with Pfizer covered all elements of biomedical innovation. He held many positions including, Senior Vice President for human health and veterinary Research and Development and Executive Vice President for Pfizer Global Research and Development. During Milne's leadership of the Research Division from 1993 to 2001, Pfizer's research investment increased five-fold from $493 million to over $2.3 billion, a number of significant products were developed, and a broad array of important new pharmaceutical products and discovery technologies were introduced. Dr. Milne was also responsible for a significant portfolio of Pfizer collaborations with prominent biotechnology companies.

"Having George Milne's insights into drug discovery as a board member and consultant provides Rib-X further competitive advantage in our drive to meet serious medical needs for new weapons against multi-drug resistant bacteria," said Susan Froshauer, Ph.D., President and Chief Executive Officer of Rib-X. "We are honored to have George as a part of the team."

"George's extraordinary record of achievement in the pharmaceutical industry is rare and will no doubt prove an invaluable resource for the Company," said Harry H. Penner, Jr., Chairman of the Rib-X Board of Directors.

Dr. Milne also serves on the boards of Charles River Laboratories, Inc., Mettler-Toledo, Inc., Athersys, Inc., the Mystic Aquarium and the New York Botanical Garden. In addition, he is a Venture Partner with Radius Ventures a health and life sciences venture capital firm based in New York. Dr. Milne received a BS in Chemistry from Yale University and his Ph.D. in Organic Chemistry from Massachusetts Institute of Technology.

About Rib-X Rib-X Pharmaceuticals is a small molecule drug discovery company focused on the structure-based design of new classes of anti-infective agents. The Company’s drug discovery strategy is focused on the exploitation of its proprietary high resolution crystal structure of the 50S subunit of the ribosome to which many known antibiotics bind. The Company’s integrated research approach combines state of the art, proprietary computational analysis, x-ray crystallography, medicinal chemistry, microbiology and biochemistry, allowing for the rapid synthesis of new agents which avoid typical antibiotic resistance mechanisms. Utilizing these tools, Rib-X is optimizing leads to create new classes of antibiotics.

Contacts Rx Communications Group Rhonda Chiger (investors) 917-322-2569 rchiger@rxir.com

Pete Holmberg (media) 917-322-2164 pholmberg@rxir.com

About Warburg Pincus Warburg Pincus is a global private equity firm and a leading investor in healthcare, biotechnology and specialty pharmaceuticals. Since 1971, Warburg Pincus has sponsored ten private equity investment funds with committed capital in excess of $19 billion. The firm is currently investing its eighth global fund, Warburg Pincus Private Equity VIII, which had a final closing in April 2002 at $5.3 billion. Warburg Pincus has invested more than $800 million in the biotechnology industry and helped to build more than 40 biotechnology and biopharmaceutical companies spanning a broad range of technologies and stages of development. For more information, please visit our website at www.warburgpincus.com.