We studied the in vitro E-selection expression of endothelial cells treated with sera from patients with Behçet's disease (BD) and factors (anti-endothelial cell antibodies, anti-neutrophil cytoplasmic antibodies, cytokines, and myeloperoxidase (MPO) that may contribute to adhesion molecule expression. A total of 21 patients with BD and 27 healthy controls were studied. In vitro E-selectin endothelial cell expression was investigated by ELISA after HUVEC incubation with sera or purified IgG from patients with BD and controls. Increased E-selectin expression was observed when endothelial cells were incubated with sera from patients with active disease or from patients with circulating anti-endothelial cell antibodies and high levels of plasma myeloperoxidase. Abnormalities of endothelial cell function have been suggested to play a role in the occurrence of vascular damage in BD. Our findings suggest that anti-endothelial cell antibodies and neutrophil hyperactivity, as inferred from the high plasma MPO levels in patients with active disease, may explain endothelial cell activation and neutrophil accumulation in vascular lesions.