In an open, non-randomized clinical trial conducted at multiple centres, 49 patients with rheumatoid arthritis were treated with recombinant interferon-gamma for 20 days. The study was carried out in two sub-studies. In the first, the total daily dose of interferon-gamma was 50 μg; in the second, 100 μg. Of the 49 cases, 40 were evaluable for statistical analysis; 24 of these patients (60%) responded to therapy, according to the criteria of a successful outcome laid down in the study protocol, and were classified as responders. In responders, the clinical parameters investigated improved with both dosages. The lower dosage differed from the higher one in having a markedly lower incidence of side-effects. The results lead to the conclusion that a randomized double-blind phase-III clinical trial should be performed.