C1 inhibitor and von Willebrand factor (vWF) levels were studied in patients with cholestatic or hepatocellular liver diseases. The vWF levels were greatly increased in hepatocellular liver diseases, whereas C1 inhibitor levels were slightly reduced. In cholestatic disease both the vWF and the C1 inhibitor levels were increased: among patients with primary biliary cirrhosis these increases were more pronounced in symptomatic patients than in asymptomatic ones. When compared with other protease inhibitors, the C1 inhibitor pattern in liver disease most closely resembled that of alpha 1-antitrypsin. Thus, C1 inhibitor levels cannot be used as a measure of residual hepatocyte mass in PBC; our data, however, suggested that antithrombin may be more suitable for that purpose.