In a controlled study involving 36 patients, thymopoietin was shown to be more effective than levamisole and as effective as penicillamine in improving the clinical status of patients with rheumatoid arthritis. There were small reductions in erythrocyte sedimentation rate and IgG which did not achieve statistical significance. Rheumatoid factor titre did not change. Although its mechanism of action is almost certainly related to its immunomodulatory properties it does not seem to be the same as that of levamisole.