Fibrinolytic disturbances are thought to play an important role in processes leading to deterioration of renal allograft function. We investigated the effect of CsA therapy on the regulation of fibrinolysis in kidney graft recipients by measuring plasma concentration and activity of plasminogen activators (tPA, uPA) and their inhibitors (PAI-1, 2). We found an increase in tPA activity and in PAI-1 concentration as well as a decrease in PAI-1 activity in renal allograft recipients as compared to healthy controls, but did not confirm a correlation between these observations and CsA administration. tPA and PAI-2 concentrations as well as uPA activity did not significantly differ between the studied groups. We showed a significant decrease in uPA plasma concentration in patients treated with azathioprine. The significance of this finding is unknown.