Fourfold intranasal administration of ATP was followed by an increase in anticoagulant activity and decrease in platelet aggregation in blood plasma of healthy rats and, particularly, of animals with suppressed function of the anticoagulant system. These changes decrease the risk of the prethrombotic state. Complex of ATP and high-molecular-weight heparin decreased platelet aggregation only in the blood from healthy animals, but increased anticoagulant potential of plasma hemostasis in prethrombotic animals.