' BioReliance Corpoi-ution, Rockville, Maryland, 20850 'Huntingdon Life Sciences, East Millstone, New Jersey 08875 3Pfjze~. Inc, Groton, Connecticut 06340 4E.~perimental Puthology Luhorator-y NorthEast, Galena, Maryland 21635 'Chernicul Industry Institute of Toxicology, Research Triangle Park, North Car-olina 27709 6Regan PathiTox Services, Ashland, Ohio 44805, and 'Covance Laboratories Inc, Vienna, Virginia 22182