1. University of Washington, Seattle, Washington 98109.
2. Children's Hospital and Medical Center of Seattle, Seattle, Washington 98105.
3. Present address: Pediatric, Adolescent, and Maternal AIDS Branch, CRMC/NICHD, 6100 Executive Boulevard, Room 4B11, MSC 7510, Bethesda, Maryland 20892-7510.
4. Boston University, Boston, Massachusetts 02215.