1. Laboratory of Comparative Carcinogenesis (Formerly Chemistry of Carcinogenesis Laboratory), National Cancer InstituteFrederick, Frederick, Maryland 21702, Environmental Toxicology and Chemistry Laboratory, Great Lakes Center, State University of New York College at Buffalo, 1300 Elmwood Avenue, Buffalo, New York 14222, and Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, The National Institutes of Health, DHHS, Bethesda, Maryland 20892