SummaryAntimitochondrial antibodies are found in 85 to 95% of patients with primary biliary cirrhosis. Nine different patterns have been identified but only four are associated with primary biliary cirrhosis. Anti-M2 antibodies are specific for the disease. The M2 antigen was found to be composed of five antigen determinants and related to the E2 component of three multienzyme complexes located within mitochondria. Anti-M4 and M8 antibodies appear invariably associated with anti-M2 and are markers for the«overlap syndrome»between primary biliary cirrhosis and chronic active hepatitis as well as for Poor prognosis. Anti-M9 antibodies are Preferentially associated with early and/or asymptomatic disease. Antinuclear antibodies are found in 24 to 58 % of patients with primary biliary cirrhosis. Six various patterns have been reported. Antibodies directed to the 200 kD polypeptide of>the nuclear pore and giving a perinuclear fluorescence are specific for primary biliary cirrhosis. Patients with such antibodies exhibit a less symptomatic disease and lower titers of anti-M2 than those without.