In a prospective randomized double-blind multicentre study cyclosporin A (CyA) and azathioprine (AZA) were compared in 117 patients with rheumatoid arthritis (starting dose CyA 5 mg/kg, AZA 1.5-2 mg/kg). The six-month treatment period was similarly completed in 92 patients with good clinical results in both groups (mean improvement rate CyA vs. AZA: Ritchie-Index 8.2 vs. 7.7, morning stiffness 41.6 vs. 28.4 min., grip strength 10.9 vs. 15.2 mmHg, swollen joint count 28.9 vs. 27.9%). Treatment was discontinued prematurely in 12 patients in each group (CyA: 2 deaths not related to drug, 1 lack of effect, 9 adverse reactions--AZA: 2 drop-outs, 1 lack of effect, 9 adverse reactions). Altogether effectivity and tolerability were equal in both treatment groups with the exception of an increase in blood pressure and serum creatinine which occurred only in the CyA group.