OBJECTIVE This study was planned to explore the alterations of endothelial functions in the prethrombotic state of Behçet's disease (BD) patients. METHODS Plasma levels of endothelial secretory markers, in vivo molecular haemostatic and fibrinolytic parameters were cross-sectionally determined in the study group. METHODS In our tertiary referral centre, 30 (13 men, 17 women) BD patients, mean age 31 +/- 7 years, and 15 (eight men, seven women) healthy volunteers, mean age 26 +/- 9 years, were eligible for inclusion in the study after obtaining their written consents. METHODS All plasma samples for the assays of haemostatic parameters were obtained before and after an endothelial stimulant, desmopressin acetate (DDAVP). RESULTS We have shown that in the procoagulant phase of BD patients: (1) basal thrombomodulin concentrations are increased and could not be provoked by DDAVP infusion; (2) both thromboxane B2 and 6-keto prostaglandin F1 alpha increments occur concurrently; (3) in vivo coagulation markers are elevated and raised plasmin-alpha 2 antiplasmin complex indicates a subclinical concomitant fibrinolysis; (4) the fibrinolytic process is conveyed in a somewhat complex manner in which plasminogen activator binding kinetics might be also altered. CONCLUSIONS Endothelial cell injury, augmented thrombotic risk with compensatory excessive fibrinolysis and alterations in endothelial cell receptor-fibrinolytic marker relations might take place in the pathogenesis and thereby modulate the natural course of haemostatic processes of BD.