1. National Institute of Public Health, University of Southern Denmark, 1455 Copenhagen, Denmark
2. Curriculum in Toxicology and Environmental Medicine, University of North Carolina, Chapel Hill, NC 27 599-7325, USA
3. Department of Epidemiology, Dartmouth Geisel School of Medicine, Hanover, NH 03 755, USA
4. Department of Epidemiology, Brown University, Providence, RI 02 903, USA
5. Department of Environmental Health Sciences, School of Public Health and Health Sciences, University of Massachusetts Amherst, Amherst, MA 01 003, USA
6. Mechanistic Toxicology Branch, Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Durham, NC 27 709, USA