1. Safety Assessment, DuPont Pharmaceuticals Company, Newark, Delaware 19714-0030, DuPont Pharmaceuticals, Stine-Haskell Research Center, Building 320, Newark, Delaware 19714-0030, .
2. Unit of Laboratory Animal Resources, University of Pennsylvania, Philadelphia, Pennsylvania 19104
3. Department of Toxicology and Pathology, Hoffinan-La Roche, Nutley, New Jersey 07110