A branched or net-like immunofluorescence pattern was demonstrated across the surface of isolated rabbit hepatocytes. We presume that this staining pattern is related to bile canaliculi on the cell surface, since it was closely correlated with the presence of bile canalicular antibodies, as detected by immunofluorescence on liver sections. Reaction with the putative bile canaliculi on rabbit hepatocytes was produced by 20 of 26 sera from patients with chronic active liver disease, 13 of 120 sera from patients with various liver diseases, and 1 of 40 normal blood donor sera.