The efficacy and toxicity of cyclosporine in the treatment of patients with rheumatoid arthritis (RA) are reviewed. Most of the early trials were restricted to patients with intractable RA. The initial daily dose of cyclosporine was 5 to 10 mg/kg, which is now considered high. Of 283 cyclosporine-treated patients in nine studies, 8% discontinued the drug prematurely because of inefficacy and 17% because of adverse reactions. Cyclosporine improves clinical parameters but does not influence the erythrocyte sedimentation rate. The most important side effects are gastrointestinal intolerance and nephrotoxicity. The former is of minor importance with the present dosage schedule (starting daily dose, 2.5 mg/kg), and increments should follow the principle "go low, go slow." Guidelines are given to avoid or reduce nephrotoxicity. It may be beneficial to administer cyclosporine early in the course of RA.