Lars Friberg, M.D., is Professor at the Department of Environmental Hygiene, Karolinska Institute, Stockholm, Sweden. Carl-Gustaf Elinder, M.D., is Associate Professor at the Department of Occupational Medicine, National Board of Occupational Safety and Health, Solna, Sweden. Tord Kjellstrom, Ph.D. (Med. Dr.) is Senior Lecturer at the Department of Community Health and General Practice, University of Auckland, Auckland, New Zealand. Gunnar Nordberg, M.D., is Professor at the Department of Environmental Medicine, Umea University, Umea, Sweden.