Ten patients with moderate to severe plaque psoriasis were treated with cyclosporin A (CyA) for 2-19 months (mean 12 months). Initial dosages were 2.5 mg/kg/d in 6 patients and 5.0 mg/kg/d in 4. At 3 months the dosage was increased from 2.5 to 5.0 mg/kg/d in 4 patients in accordance with the study protocol. Subsequent dosages were adjusted according to clinical response and side-effects. Treatment was stopped owing to raised serum creatinine levels in 4 patients on the higher dose; levels returned to normal soon after this. The only other important side-effect was hypertension, which developed in 4 patients, in 2 of whom serum creatinine levels were raised. In all patients the psoriasis improved markedly within 2 months but relapsed, either while the dose of CyA was being tapered off or after treatment with the drug was stopped. Relapse was most rapid in patients with severe initial involvement. On a dosage of 2.5 mg/kg/d there was at least 50% clearance of the psoriasis and no evidence of renal side-effects.