1. From the Department of Medicine, University of Colorado School of Medicine, Denver, CO, the departments of Pathology, Medicine and Clinical Epidemiology and Biostatistics, McMaster University Medical Centre, Hamilton, ON, Canada, and the Division of Hematology, Department of Medicine, Harborview Medical Center, University of Washington School of Medicine, Seattle, WA 98105 (address reprint requests to Dr. Genton at the University of Colorado Medical Center, 4200 E. 9th Ave., Denver, CO 80220).