Eight patients with psoriatic arthritis entered an open study to determine the efficacy of oral cyclosporin A for their treatment. The starting dose was 3.5 mg/kg daily. Findings after the first six months are reported. One patient withdrew from the study after five months because of tremors, general malaise, and lack of improvement. Seven patients continued through the study, and marked improvement was found after two months in all clinical indices. The skin lesions improved in a parallel fashion. The cyclosporin A dose had to be reduced temporarily by 25% in three patients because of an increase in serum creatinine of more than 50%. A rise in diastolic blood pressure in three patients responded to treatment. The study suggests that cyclosporin A effectively treats arthritic manifestations of psoriasis as well as psoriatic skin lesions.