Children who participate in the study are evaluated at a hospital outpatient clinic and are under the care of a specialist in pediatrics. Of the children who participate in the study, half receive AZT syrup and half receive a placebo (sugar solution). The investigator does not know which medication each child receives as this is decided by a random process. The children take the medication in a strawberry-flavored clear syrup every 6 hours (4 times a day), for a period of 2 years or 104 weeks. The children are monitored on an outpatient basis while receiving therapy and the tests performed on admission to the study are repeated several times during treatment. Blood samples are obtained once a week for the first 4 weeks, every other week for the next 4 weeks, and then monthly until the end of the study. At certain sites, Cerebrospinal fluid (CSF) is collected by lumbar puncture every 52 weeks to evaluate infection involving the brain and nervous system. An independent committee reviews the data collected on the children every 6 months. The drug is stopped or the dose reduced if unacceptable side effects develop. AMENDED: As of August 7, 1989 the study blind was broken, the placebo arm discontinued and the study closed to accrual as of September 25, 1989. The 6 children enrolled in the study have been offered AZT.