Immunological and viral studies were conducted on cerebrospinal fluid from 31 HIV-1-infected children, of whom 23 were neurologically asymptomatic and 8 had progressive encephalopathy. After AZT treatment, a second cerebrospinal fluid specimen was obtained from 15 children, 11 of whom were neurologically asymptomatic and 4 had progressive encephalopathy. Virus isolation and p24Ag detection were more frequent in children with progressive encephalopathy than in asymptomatic children (66% versus 12%) and were inversely correlated with intrathecal HIV-1-antibody detection (anti-gag AB: 25% versus 70%). High concentrations of interleukin-1β (IL-1β) and IL-6 were found in children with progressive encephalopathy (50% and 37%, respectively), but low levels were also detected in some asymptomatic children (13% and 9%, respectively). Tumour necrosis factor-α (TNFα) was not found. AZT treatment induced disappearance of p24Ag in cerebrospinal fluid, as well as a marked reduction in cytokine levels. Cytokine determination may be useful in monitoring AZT treatment in children with progressive encephalopathy.