['Patients with primary biliary cirrhosis (PBC) frequently produce autoantibodies against constituents of the nuclear envelope. We have recently observed a reactivity of PBC sera with a nuclear envelope antigen at approximately 60 kilodaltons. The aim of this study was to characterize the reactive antigen.', 'Sera from 103 patients with liver disease were tested by immunoblotting after the separation of proteins by one- and two-dimensional polyacrylamide gel electrophoresis (PAGE) using proteins of whole nuclei and nuclear pore complexes (NPCs).', 'A nuclear immunofluorescence staining with peripheral accentuation was observed in 25 of 43 sera from patients with PBC. In immunoblotting, the sera displaying a peripheral pattern reacted preferentially with two proteins. Twelve sera showed specificity to an antigen of 210 kilodaltons corresponding to gp210, and 14 sera recognized a protein band at 60 kilodaltons. The intensity of the reactive band at 60 kilodaltons was clearly stronger on blots with immobilized proteins of the NPC than on blots with nuclear proteins, thereby indicating that the sera targeted an antigen as being a component of the NPC. Immunoblotting performed after protein separation by two-dimensional PAGE showed that the sera are directed against nucleoporin p62, a functional protein of the NPC.'] Do autoantibodies against nucleoporin p62 constitute a novel marker of primary biliary cirrhosis?