1 IV dose and 1 oral dose followed by 6 weeks of oral AZT (4 doses per day) and a second IV dose at the end of the study. Each child is under the care of a specialist in pediatrics and has a physical examination and laboratory tests before starting AZT and 6 times while taking AZT to make sure the drug is not having a toxic effect on the child. A single cerebrospinal fluid (CSF) sample is taken from the last 12 children entering the study, so that the level of the AZT reaching the brain can be measured. The child returns to the hospital or clinic 4 weeks after the end of therapy to make sure that there are no delayed toxic effects.