In chronic experiments on 75 Wistar, August and randombred rats hemodynamic changes were examined during 30-hour immobilization stress. The ECG was recorded and arterial blood pressure measured. The basic hemodynamic characteristics were determined with the help of the previously implanted ultrasonic blood flow probes. Analysis of hemodynamic changes in animals resistant, adapted and prone to stress demonstrated that changes in the total peripheral resistance play the leading role in the disturbance of the arterial blood pressure control. It was established that a progressive lowering of arterial blood pressure resulting from the abruptly reduced total peripheral resistance is the main and the most frequent cause of death of animals exposed to immobilization stress. At the same time the cardiac hemodynamic component may play an essential role in the mechanism of death. This component may include either progressive bradycardia or a combination of an ischemic myocardial damage and reduced total peripheral resistance.