Fibrinolysis of bone marrow aspirates and peripheral blood from patients with various blood diseases was studied by thrombelastography. The fibrinolytic rate of bone marrow aspirates was compared with that of peripheral blood, and it was disclosed that the fibrinolytic activity of the former was always higher than that of the latter at 1 and 2 hours of observation. Alteration of the fibrinolytic activity of bone marrow aspirates preceded that of peripheral blood in accordance with the clinical conditions of diseases. This tendency was pronounced in some cases of acute leukemia. It was also demonstrated that addition of antiplasmin agent such as ε-ACA and trans-AMCHA clearly suppressed the fibrinolytic activity. A few cases of ITP, pure red cell aplasia, ALL and Banti's syndrome were found to exhibit a new pattern of thrombelastogram.