We treated six patients with moderate to severe skin symptoms of Behçet's disease with oral administration of Cyclosporin A (CsA). During the first two weeks, 5 mg/kg/day CsA twice a day was given and then the dose was reduced to 3 mg/kg/day. Erythema nodosum like eruptions, oral aphtha, and thrombophlebitis began to improve within three days, and four patients had complete remission by two weeks after the start of treatment. In one patient, a genital ulcer took almost three months to disappear. In peripheral blood of patients treated with CsA 5 mg/kg/day for two weeks, there were decreases in the OKT4/OKT8 ratio. After the reduction of the dosage, the ratio was temporarily increased, but it decreased to the normal range around the twelfth week of the treatment. No clinically important side effects were seen.