The procoagulant activity of antihemophilic factor (AHF-Ac) and AHF-like antigen (AHF-Ag) level in liver diseases have not been well studied, although it has already been shown that the level of vitamin K dependent clotting factors such as prothrombin, factors VII, IX and X is a very sensitive parameter of liver function.We studied AHF-Ac and AHF-Ag in 13 patients with acute hepatitis (AH), 15 with chronic active hepatitis (CAH), 20 with compensated liver cirrhosis (CLC) and 16 with decompen-sated liver cirrhosis (DCL). Also were performed coagulation studies in the same patients, such as hepaplastintest, prothrombin time, kaolin-activated PTT and assays of fibrinogen, prothrombin, factors V and IX.Hepaplastintest was normal in the majority of patients with AH, whilst many cirrhotic patients showed abnormal value. Prothrombin time and APTT were also within normal limits in the majority of cases of AH, CAH and CLC. Level of prothrombin and factor IX was proved to be a good parameter of liver function, although that of fibrinogen and factor V was insensitive to liver damage.AHF-Ac and AHF-Ag were both increased in almost all patients with the hepatic disorders mentioned above. The mean values of the AHF-Ac were 257±139% in AH, 124±53% in CAH, 104±30% in CLC and 189±74% in DLC, whilst those of AHF-Ag were 190±89%, 189±50%, 207±56% and 344±191% respectively.AHF-Ac in cirrhotic patients correlated well with serum γ-globulin level (p<0.01) and also was there close correlation between AHF-Ac and serum bilirubin level in patients with AH, but not statistically significant.The AHF-Ac/AHF-Ag ratio in patients with AH was 1.53±0.94, in contrast to 0.70±0.31 in CAH, 0.54±0. 24 in CLC and 0.63±0.27 in DLC, which showed higher level of AHF-Ac than that of AHF-Ag in AH.The cause of increased level of AHF in hepatic disorders still remains unknown, although increased extrahepatic production of AHF due to stress states and delayed inactivation and clearance of this factor in the liver may be playing a main role.