Ampligen, poly(I)n:poly(C12U)n, was administered intravenously to 39 human immunodeficiency virus (HIV)-infected subjects, asymptomatic or with early AIDS-related complex (ARC) and with CD4+ cell counts less than 500/mm3 in a phase I dose-escalation study. Six doses ranging from 10 to 570 mg/m2 were administered twice-weekly for 9-25 weeks to groups of 5-7 subjects. There was no significant effect on HIV as measured by serum p24 levels, the proportion of patients from whom HIV could be cocultured from blood, or the concentration of peripheral mononuclear cells positive for the virus. Although patients on 10 and 40 mg/m2 showed a significant decline in CD4+ cell counts, as would be expected in untreated patients, patients who received doses greater than or equal to 120 mg/m2 showed no significant decline in CD4+ cell counts. In addition, there was a significant increase in CD4+ cell counts with respect to dose of ampligen. This effect of ampligen and the fact that it has been shown to act synergistically with zidovudine against HIV in vitro suggest that the combination might be tried clinically in patients.