Sixteen patients who had shown a good clinical response to cyclosporine therapy during a randomized 6-month double blind study comparing cyclosporine with D-penicillamine in active rheumatoid arthritis, had an opportunity to participate in an open study with cyclosporine. The initial daily dose of cyclosporine was 5 mg/kg. Before the planned maximal duration of 18 months, there were 6 premature discontinuations, 2 because of inefficacy, 2 because of side effects, and 2 for other reasons. During the study there was an improvement in all clinical variables. Even under the strict conditions of our trial there was an irreversible loss of about 15% of renal function. Suggestions are given to minimize the chance of nephrotoxicity.