It has been postulated that Behçet's disease may be a viral induced vasculitis. In the present study plasma exchanges were applied in an attempt to remove circulating immune complexes and restore cellular immunity. High doses of acyclovir were administered in association with plasma exchanges since it has been shown that herpes simplex virus type 1 might be involved in Behçet's vasculitis. Seven patients with severe ocular manifestations of Behçet's disease were selected for the study. Plasma exchanges were carried out at the rate of 3 per week during 3 weeks and then once every two weeks during 3 months followed by 1 per month during 3 months. 45 mg/day/kg acyclovir were administered intravenously for 21 days. At the end of the follow-up period comparative analysis of panretinal fluorescein angiographies before and after treatment showed no change of the fundus lesions in 3 patients, improvement in only 2 patients and significant worsening in 2 patients. The rather negative results of the present trial lead to assume that HSV-1 is not the virus involved, if any, in Behçet's disease. On the other hand, in the present study, the efficiency of plasma exchanges was transient.