The role of biliary epithelial cell (BEC) antigens in immune recognition and damage of biliary epithelium in primary biliary cirrhosis (PBC) is unknown. The major autoantigen in PBC (the mitochondrial enzyme pyruvate dehydrogenase dihydrolipoamide acetyltransferase [PDC-E2]) is abnormally distributed in the biliary epithelium of patients with PBC relative to controls. The antigen is not only present in mitochondria but also associated with the BEC plasma membrane. This atypical distribution of PDC-E2 is present both in early (stages I-II) and advanced (stages III-IV) disease, suggesting a role for the antigen in progression and/or etiology of PBC. The identity of the plasma membrane antigen remains unknown, but there is evidence to suggest that it is an antigen that cross reacts with antibodies to PDC-E2. Use of BEC purified from human liver may help in deciphering the possible importance of BEC plasma membrane antigens in immune recognition and toxicity toward BEC in PBC.