A 6 month open trial of cyclosporine (CyA) was conducted in 20 patients with active rheumatoid arthritis unresponsive to second line therapy. The dosage was monitored to achieve a serum blood level of 75-150 ng/ml. A 25% reduction in ARA joint count (baseline mean 38.2; 6 month or time of CyA withdrawal mean 28.7; p less than 0.001) was observed for all patients. Fifteen completed the 6 month CyA regimen and 5 developed toxicity requiring CyA to be permanently withdrawn. For the 15 patients completing 6 months of CyA, improvement was 36% (baseline 34.7; 6 month mean 22.2; p less than 0.001). Corresponding improvements were also observed on the other main study outcomes of pain and functional ability. Improvement occurred between 12-20 weeks, somewhat later than in other studies. Toxicity included mild hypertension (4 patients) and gastrointestinal intolerance (2). Three patients were withdrawn from CyA due to nephrotoxicity. There was a clinically significant reduction in calculated creatinine clearance but this returned to baseline within 6 months after CyA was withdrawn for all except 2 patients who took 12 months to return to baseline.