1. Intramural Research Support Program, SAIC Frederick, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, Maryland 21702, Salt Lake City Veterans Administration Medical Center, Salt Lake City, Utah 84148, Department of Chemistry, George Mason University, Fairfax, Virginia 22030, and Chemistry Section, Laboratory of Comparative Carcinogenesis, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, Maryland 21702