Anhepatic stage in livertransplantation are accompanied by various coagulation disturbances. Coagulation changes during the anhepatic stage were investigated in hepatectomised dogs. Animals were divided into 3 groups; Group I with total hepatectomy under the V-V bypass using pump without heparinization, Group II with V-V bypass only and Group III with splenectomy only. The platelet count was not changed in Group III but decreased significantly in Groups I and II from 30 minutes after start of V-V bypass. The platelet aggregability was lowered with time in Group I, but stayed unchanged in Group III. Prothombin time (PT) was significantly prolonged in Group I from 30 minutes after V-V bypass start, compared to Group II. The fibrinogen degradation products (FDP) were positive in 40% of the Group I dogs at 30 minutes after V-V bypass start, but became positive in 100% after 3 hours. The positive ratio in Group III did not changed with time. Analysis of the coagulation changes by V-V bypass suggested that at the anhepatic stage, plasma clotting factor deficiencies occur relatively early with the appearance bf FDP resulting in coagulation disturbances.