Twelve patients with active Behçet's uveitis with marked deterioration of visual acuity in at least one eye were treated with cyclosporin A (CyA). An initial improvement in the severity of ocular inflammation and systemic features occurred in all cases and persisted until the dose was reduced or the drug withdrawn when a rapid recurrence of symptoms was noted. The visual acuity also initially improved in ten patients and this was maintained in seven cases until the dose of CyA was reduced. At this time, acuity was unchanged in two patients and was worse in three others-two of the latter as a result of vitreous haemorrhage in the absence of active inflammation. Seven of the 12 patients had therapy stopped because of complications; severe malaise and nausea (three cases), decreased renal function (three cases), and blindness (one case). Cyclosporin A is of value in the control of Behçet's uveitis but toxicity limits its use and the benefits only last while the patient is on this therapy.