1. Department of Radiation Medicine, Vincent T. Lombardi Comprehensive Cancer Research Center, Georgetown University Medical Center, Washington 20007.
2. Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20992.
3. Michael Reese Hospital, University of Chicago Center for Radiation Therapy, Pritzker School of Medicine, University of Chicago, Chicago, IL 60637.
4. Merck, Sharp and Dohme Research Laboratories, Rahway, NJ 07065.