Behcet's disease is characterized by orogenital ulcerations and ocular lesions. Other features include arthritis, thrombophlebitis, neurological abnormalities and skin lesions. The disease is characterized by a relapsing inflammatory process of unknown aetiology. Lipoprotein(a) is an LDL-like particle with a large glycoprotein called apolipoprotein(a) attached to its apolipoprotein B moiety through one or more disulphide bonds. Apolipoprotein(a) is related to plasminogen from which the enzyme plasmin, that hydrolyses fibrin blood clots, is released by tissue plasminogen activators. The unique structural features of Lp(a) give it the potential for atherogenic and thrombogenic activities. In the present study 35% of patients with Behcet's disease were shown to have higher Lp(a) concentrations than the cut-off point (0.30 g/l) for atherosclerosis. Plasma Lp(a) concentrations in the remission period were also found to be lower than during the active period in the same patients (23% decreased). Lp(a) showed significant correlations with acute phase reactants such as erythrocyte sedimentation rate, polymorphonuclear leukocytes and polymorphonuclear leukocyte elastase activity. Therefore, it was concluded that the fluctations of plasma Lp(a) levels with the activity of disease may be a contributing risk factor in the development of thrombogenic complications in patients with Behcet's disease.