1. From the Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, the Department of Medicine, Veterans Administration Medical Center, the Departments of Medicine and Pathology, Abbott–North-western Hospital, and the Department of Medicine, Hennepin County Medical Center, Minneapolis. Address reprint requests to Dr. Yunis at the Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Box 198 Mayo Bldg., 420 Delaware St., Minneapolis, MN 55455.