This study was designed to evaluate local alterations of the fibrinolytic process in patent-functional native arteriovenous fistulas of patients on maintenance haemodialysis. For this aim, the concentrations of the main components of the fibrinolytic system were determined in plasma samples taken simultaneously from arteriovenous fistulas and contralateral upper extremity concurrent large veins of haemodialysis patients. Twelve patients (6 women and 6 men, age 36 +/- 8 years) with end-stage renal disease on maintenance haemodialysis and 15 non-smoker healthy volunteers (8 women and 7 men, age 31 +/- 10 years) with normal renal function were included in the study. The fibrinolytic parameters, except alpha 2-antiplasmin, were found to be elevated in arteriovenous fistulas of haemodialysis patients as compared with opposite upper extremity large veins of the same patients (p < 0.005). Increments in fibrinolytic parameters including tissue plasminogen activator antigen, urokinase-type plasminogen activator antigen and activity, and plasminogen activity together with lower alpha 2-antiplasmin levels favor activation of fibrinolysis, except for higher alpha 2-macroglobulin concentrations, in arteriovenous fistula. The study suggests that the fibrinolytic process is locally activated in arteriovenous fistulas of haemodialysis patients.