Cyclosporine may be useful in the treatment of rheumatoid arthritis refractory to other immunosuppressive agents, in doses of less than 10 mg/kg/day to minimize its nephrotoxic potential, that is enhanced with prolonged use or concomitant administration of anti-inflammatory drugs. We report 15 patients aged 50 +/- 12 years with erosive rheumatoid arthritis lasting 5 +/- 4 years and refractory to other immunosuppressive agents. They were studied during one year and received cyclosporine in initial doses of 2.5 mg/kg/day that were increased to 5 mg/kg/day, assessing clinical response, blood pressure and serum creatinine. Nine patients, that received a maximal dose of 3.4 +/- 0.7 mg/kg/day during 7 +/- 4 months, improved; a 30% increase in creatinine was observed in 3, blood pressure raised in six and two had hepatic toxicity. In the six patients that did not improve, the mean treatment lapse was 4 +/- 3 months and the maximal dose achieved was 2.7 mg/kg/day; creatinine increased in one and blood pressure increased in 4. It is concluded that although the clinical response to cyclosporine was good, only 4 patients completed one year of treatment, due to the frequent secondary effects of the drug.