The process of clinical development and regulatory review of new therapeutics in the United States was significantly changed by a number of legislative acts passed in the 1980s and 1990s. These acts were designed to encourage the development of innovative products, especially for rare, serious or life-threatening diseases, and to ensure that patients had timely access to these treatments. To assess the effects of the various modifications to the process, the Tufts Center for the Study of Drug Development analysed clinical development and approval data for 554 therapeutics (504 small molecules, 40 recombinant proteins and 10 monoclonal antibodies) approved in the United States from 1980-2001. Trends in the number of approved products and the clinical development and approval times indicated that the effects of these changes were generally beneficial as of the mid- to late-1990s, but that the gains have not been sustained in the early 2000s. Current efforts by the FDA, and the pharmaceutical and biopharmaceutical industry, to reverse the recent tendency toward fewer new approvals and longer approval times are discussed.