The englobulin fraction was extracted from bone marrow aspirates and peripheral blood of patient with various blood diseases. The fibrinolytic activity of this fraction was measured by the standard and heated fibrin plate method. The fibrinolytie activity of bone marrow aspirates was found to be always higher than that oｆ peripheral blood in normal and pathological conditions. The level of plasminogen activator of bone marrow aspirates was also higher than that of peripheral blood, particularly in leukopoietic and thrombopoietic disorders as well as in dysproteinemias. This finding suggested that plasminogen might be activated to plasmin in bone marrow.