Azathioprine has been shown to reduce the steroid requirements of patients with severe rheumatoid arthritis. Twenty-seven patients treated with azathioprine have now been followed up for 30 months. At the end of this period only 10 were still taking the drug. Maximum steroid reduction occurred within the first 12 months of treatment. Some steroid-sparing effect seemed to persist after the drug was stopped. There was no evidence that azathioprine prevented radiological deterioration. No deaths occurred and toxic effects always reversed on stopping the drug.