In the present study, we have shown considerably accelerated thrombosis in old rats in comparison with adult rats, which may be related to the impaired hemostatic balance in these animals. In old rats, captopril and enalapril caused a marked reduction of venous thrombus weight. The mechanism of antithrombotic action of these drugs seems to be dependent on the suppression of coagulation cascade and the enhancement of the fibrinolytic processes.