Behçet's disease is a chronic multisystemic disorder. It is characterized by a relapsing systemic inflammatory process. Thrombosis is one of the vascular manifestations and is closely affected by endothelial dysfunction resulting from the degree of perivascular inflammatory process. The present study was carried out to determine if plasma PMN elastase may be a good marker for evaluation of endothelial status in the Behçet's patients who are in active and inactive phases. The parameters including PMN elastase, t-PA, PAI-1 and other markers related to activity of the disease such as ESR, PMN leukocyte count, alpa-2-globulins were determined in the twelve patients and ten healthy volunteers as a control group. The mean PMN elastase levels in both the active and inactive phases of the disease were found to be higher than that of control group. Reduced t-PA and increased PAI-1 level of the patients during the active phase were observed as compared with those inactive phase of the disease. PMN elastase showed a negative correlation with t-PA and a positive correlation with PAI-1 levels both in the active and inactive phase of the disease. The relationships between PMN elastase and t-PA and PAI-1 may results from the possible effects of the increased activity of PMN leukocytes to endothelial cells. It was concluded that plasma PMN elastase levels may be a well-characterised and sensitive inflammation marker for reflecting activity of the disease, and also its association with endothelial dysfunction.