1. Division of Hematology of the Department of Medicine, Children‘s Hospital Medical Center, the Department of Pediatrics, Harvard Medical School, Boston, Mass. 02115.
2. Peter Bent Brigham Hospital, Boston, Mass. 02115.
3. Harvard Medical School, Boston, Macc. 02115.
4. Children's Hospital Medical Center; Assistant Professor of Pediatrics, Harvard Medical School, Boston, Mass. 02115: Recipient of Research Career Development A ward, AM-70234, of the National Institutes of Health. Bethesda, Md.