When ocular structures are affected in Behçet's syndrome, a rapid loss of vision has been the rule regardless of the type of treatment--corticosteroids, Leukeran, Imuran, colchicine. The objectives of the present study were to compare, in a masked manner, conventional treatment (corticosteroids/Leukeran) to treatment with CsA. Forty patients suffering from Behçet's syndrome with active ocular inflammatory reactions were included in the study. These were randomly assigned to conventional or CsA regimens and were regularly examined by a multidisciplinary group of physicians. The unmasked internist modulated the treatment and recorded systemic manifestations. The masked ophthalmologists recorded the ocular findings without knowledge of the assigned type of treatment. An analysis of the results 3 years after initiation of the study shows that CsA is more effective than conventional therapy in decreasing the active ocular inflammatory processes and arresting the deterioration of visual acuity. Regarding the extraocular symptoms, however, conventional therapy is superior to CsA, especially for the control of skin lesions and arthritis. Side effects were recorded in a much higher incidence among patients receiving CsA. However, tight and constant control of the CsA dosage as performed in this study has, so far, prevented clinical and biochemical nephrotoxic manifestations in patients assigned to this treatment.