It was discovered that adult rats develop hypercoagulation and inhibited fibrinolysis 2--4 months after thymectomy. Intramuscular injections of thymus low-molecular factor to thymectomized rats for a week made the coagulative and fibrinolytic activity of blood return to normal. After adrenaline injection, the sham-operated rats developed hypercoagulation and stimulated fibrinolysis. In thymectomized rats, fibrinolysis was stimulated far less after adrenaline injection and did not reach the levels characteristic of the sham-operated rats. The thymectomized rats given thymus factor manifested an appreciable recovery of an adequate response on the part of blood coagulation and fibrinolysis to adrenaline injection.