1. From the Department of Pathology, University of Massachusetts Medical School and Bay State Medical Center, the Department of Pediatrics of the Dartmouth Medical School, Hanover, NH, and the Mallory Institute of Pathology, and the Cancer Research Center, University of North Carolina at Chapel Hill (address reprint requests to Dr. Purtilo at the Department of Pathology, University of Massachusetts Medical School, 55 Lake Ave., North, Worcester, MA 01605).