Primary biliary cirrhosis (PBC) of the liver is considered to be an autoimmune liver disease in which an immune aggression is directed against small biliary ducts--mitochondrial antigens of a biliary epithelium. The targets of an immune aggression in PBC may also be the histocompatibility antigens of the biliary ducts epithelium. This makes PBC resembling so-called disease "graft against host". The destruction of bile ducts in PBC is brought about through the mechanisms of an immune cytolysis and is manifested morphologically by the symptoms of the delayed hypersensitivity response. Cholangiole proliferation develops along the ductal destruction, sclerotic changes and cholestasis increase in their intensity. Small-nodular cirrhosis develops at the final stage of disease. Systemic manifestations of PBC are associated with a circulation of immune complexes containing hepatobiliary antigens. Cross-immune reactions are also of importance in the mechanisms of extrahepatic lesions.