Letter from Elaine C. Esber (Acting Director, Office of Biologics Research and Review, national Center for Drugs and Biologics) and Harry M. Heyer (Director, National Center for Drugs and Biologics) to Steven J. Ojala (Miles Laboratories, Inc). Discusses approval of Antihemophilic Factor (Human) product license to include a heat treatment step and asks for preliminary results of ongoing chimpanzee and stability studies relating to infectivity.