News Pressroom

November 19, 1999

MedImmune to Exchange 0.15 Shares for Each U.S. Bioscience Share in Proposed Acquisition

Gaithersburg, MD, and West Conshohocken, PA, November 19, 1999 --- MedImmune, Inc. (Nasdaq: MEDI) and U.S. Bioscience, Inc. (Amex: UBS) announced today that each share of U.S. Bioscience common stock will be exchanged for 0.15 shares of MedImmune common stock in the previously announced proposed merger of the two companies. Any fractional shares of U.S. Bioscience stock will be paid in cash.

The exchange ratio was based on MedImmune's average closing price of $106.36 over a 20-day trading period that ended on November 18th, three trading days prior to the U.S. Bioscience Special Meeting of Stockholders, being held to consider the acquisition. The Special Meeting is scheduled for 10:00 a.m. EST on November 23, 1999. Completion of the merger, if approved, is expected to occur shortly after the Special Meeting.

The offering of MedImmune common stock in connection with the merger is made under an effective S-4 Registration Statement. The offering is being made only by means of a proxy statement/prospectus relating to the merger, which has been distributed to U.S. Bioscience stockholders.

MedImmune, Inc., located in Gaithersburg, Maryland, is a biotechnology company focused on developing and marketing products that address medical needs in areas such as infectious disease, transplantation medicine, autoimmune disorders and cancer.

U.S. Bioscience, Inc., based in West Conshohocken, Pennsylvania, is a pharmaceutical company specializing in the development and commercialization of products for patients with cancer and AIDS.

Statements about the proposed merger are forward-looking statements that involve risks and uncertainties. Among the factors that could cause actual results of MedImmune, U.S. Bioscience or the combined company to differ materially from those in the forward looking statements are: the failure of the merger to be consummated, the ability of the companies to successfully integrate, challenges inherent in new product development and marketing, governmental laws and regulations, including possible healthcare reform, the availability of favorable tax and accounting treatment for the merger and those factors in the companies' reports and filings with the U.S. Securities and Exchange Commission. The companies disclaim any intention or obligation to update or revise any forward-looking statements.