We propose that thrombosis in Behçet's syndrome may be due to disruption of the annexin V shield by antiphospholipid antibodies. Measurement of antiannexin V antibodies may be of value in confirming diagnosis and evaluating the risk of venous and arterial thrombosis in patients with Behçet's syndrome. To evaluate the efficiency of antiannexin V antibody in the formation of thrombosis, 53 male patients with Behçet's disease according to international study group criteria were involved in this study. The age range was 20-28 years (mean 23+/-3.4). All of these patients had been taking colchicum. Those taking medications that interfere with antiannexin V autoantibody levels were excluded, and serum samples were taken during the active period. Group I included 26 Behçet's patients with well-documented thrombosis, group II included 27 Behçet's patients without thrombosis, and group III was comprised of 27 healthy controls. There were no statistical differences between the mean concentrations of IgG and IgM antiannexin V autoantibodies in the three groups. The results indicate that these antibodies may not be associated with the pathogenesis of thrombotic events in patients with Behçet's syndrome.