During one year experiment, the thromboplastic, antiheparin, plasminogen activator, antithrombin and antiplasmin activities were evaluated in the homogenates of the intimal, medial and adventitial layers of polyester double velour DALLON prostheses implanted into the dog abdominal aorta. It was found, that 7 days after implantation the thromboplastic, antiheparin and plasminogen activator activities in DALLON graft neointima were high, whereas those of the antiplasmin and antithrombin were low. These changes facilitate the sealing of the prosthesis pores and at the same time prevents thrombosis. Four months after implanting, the activity of hemostatically active components in the various graft layers became similar to the activity of aorta components. Rapid decrease of the thrombogenic potential and increase of the fibrinolytic activity in layers of double velour DALLON grafts facilitate the maintenance of graft patency.