1. Division of Biochemical Toxicology, National Center for Toxicological Research, Jefferson, Arkansas 72079, National Institute of Environmental Health, József Fodor National Center for Public Health, Budapest, H-1097, Hungary, Béla Johan National Center for Epidemiology, Budapest, H-1529, Hungary, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, and National Institute for Occupational Health Safety, Centers for Disease Control and Prevention, Morgantown, West Virginia 26505