The controlled clinical trial reported here is part of a multicenter clinical and basic research project, sponsored by the German Federal Minister of Science and Technology, directed by a standing commission of the president of the Max-Planck-Gesellschaft, and coordinated by the Max-Planck-Institut für Biochemie, München. Overall, 249 patients with rheumatoid arthritis (RA) were enrolled by 16 participating hospitals. In addition to NSAID treatment, patients were randomly given either interferon gamma (IFN-gamma) or placebo. In the IFN-gamma group, 107 patients were evaluated and in the control group, 116 patients were evaluated. The response rate after 3 months of treatment, according to joint pain indexes, was significantly higher in the IFN-gamma group with an error probability of 1%. IFN-gamma was able to reduce the quantity of corticosteroids administered. Compared with the control group, the IFN-gamma group benefited considering all parameters measured. Most important side effects were transient fever and transient influenza-like symptoms; all other adverse events were comparable in both groups.