The present study demonstrates that the fibrinolytic activity is significantly increased and the level of plasminogen antiactivator diminished in the blood of patients with advanced liver cirrhosis and chronic aggressive hepatitis as compared with the values for healthy subjects. Total fibrinogen concentration was similar in patients and controls. However, electrophoresis of plasma with the use of SDS-polyacrylamide gel (3.5%) showed considerable differences in the composition of fibrinogen fractions. Lower molecular weight (LMW and LMW1) clottable protein was significantly (p less than 0.01) increased in the patients. In two out of 22 patients the higher molecular weight (HMW) fraction was virtually absent. In vitro incubation (37 degrees C for 48 hr) of diluted (1:10) plasma from a patient resulted in extensive degradation of a low-solubility fibrinogen fraction (HMW) previously added to the sample. No degradation was observed in any undiluted plasma samples. It is concluded that the increased concentration of lower-molecular-weight forms of clottable protein in the blood of patients with liver disease is probably related to increased in vivo degradation rather than abnormal synthesis. An association rather than a direct correlation with fibrinolytic activity was found.