Twelve patients with refractory rheumatoid arthritis were included in a 1-year open trial of cyclosporin A (CsA), 5 mg/kg/day. Clinical efficacy was observed 1 month after beginning treatment, was well established after 4 months of therapy, and remained stable for the remainder of the 1-year treatment period. Among the numerous side effects observed, renal toxicity and hypertension occurred suddenly during the trial and required constant monitoring, adequate therapy, and modulation of CsA dosage. Cyclosporin A seems to be an effective treatment for active rheumatoid arthritis, but it requires close monitoring for toxicity.