Fourteen patients with Behçet's disease and bilateral eye involvement were treated for periods of between 30 and 38 months with low doses (5 mg/kg/day) of cyclosporin A (CyA). In patients who responded well, this dose was reduced to a maintenance dose of 2 mg/kg/day. There was a good response to treatment in 86% of patients, with complete disappearance of ocular attacks in 43% and a reduction in frequency and severity of attacks in a further 43%. Only one patient suffered a deterioration in visual acuity (0.2 in one eye) during treatment. The visual acuity of all the other patients (93%) either remained the same or improved. Attacks of buccal and genital aphthous ulceration were also less severe and less frequent during treatment with CyA, although they were proportionally more frequent than ocular attacks. The main side effects were a dose-dependent and reversible biochemical renal toxicity in 28% of patients, gingival inflammation in 14% of patients, and systemic arterial hypertension in 7% of patients. Hirsutism was observed in 100% of the female patients. We conclude that low doses of CyA administered over a long period of time constitute an effective therapeutic alternative that helps prevent evolution towards blindness in Behçet's disease, although it has the disadvantage as compared with chlorambucil that it does not inactivate the disease. The anti-inflammatory effect is therefore dose-dependent and persists only for as long as the drug is being administered.