To assess the efficacy and safety of ribavirin in patients with human immunodeficiency virus (HIV) infection a multicentre, placebo-controlled, prospectively randomised trial was conducted in CDC group III HIV-infected individuals between February, 1988, and October, 1989. Mean treatment time was 39 weeks (range 6-52); 152 individuals were enrolled, of whom 133 could be evaluated. The two treatment groups were similar at baseline and 66% of all subjects had intravenous drug abuse as the main risk factor for HIV infection. Ribavirin was given at a dose of 15 mg/kg daily by mouth (average daily dose 1000 mg). 9 of 67 patients in the placebo group (13.4%) progressed to CDC Groups IVA, C1, or D vs 6 of 66 (9%) in the ribavirin group. Progressions to group IVC2 were 7 (10.4%) and 9 (13.6%), respectively. These differences are not statistically significant. There were no clinically or statistically significant differences in CD4 cell counts, total lymphocytes, total white cells, or CD4/CD8 ratios between the two groups during treatment, and no clinically important side-effects were noted.