In a controlled study involving thirty-four patients levamisole was shown to be as effective as D-penicillamine and more effective than placebo in the treatment of rheumatoid arthritis. Its action was slow and was accompanied by a reduction in erythrocyte sedimentation-rate, rheumatoid factor, and technetium index. These properties indicate that it has a specific action like that of D-penicillamine. Stimulation of cell-mediated immunity was evident in patients treated with levamisole, and there was a correlation between such changes and pain relief. Animal models confirmed the absence of anti-inflammatory effect and provided some evidence of enhancement of cell-mediated immunity and macrophage stimulation.