We investigated the effects of the hapten trinitrobenzenesulfonic acid instilled into the rat biliary tree. The study included three groups of animals that received a single intracholedochal injection of either saline, 10% ethanol or 10 mg trinitrobenzenesulfonic acid dissolved in 10% ethanol. A fourth group of rats was subjected to common bile duct ligation and was used as control for biliary obstruction. Liver and biliary tract dysfunction was assessed 1, 10, 20 and 30 days after treatment by serum aspartate aminotransferase, alkaline phosphatase and bilirubin, and by histopathological examination of liver slices. By day 10, saline- or ethanol-treated rats did not show changes in the biochemical parameters, and light microscopy revealed no alterations. In contrast, rats treated with trinitrobenzenesulfonic acid showed significant increases in all serum markers throughout the study period. Inflammatory cell infiltrates were seen in portal areas and around bile ducts, indicating pericholangitis. Some rats presented with dilatation of extrahepatic biliary ducts; ductal proliferation and thin porto-portal fibrotic septa were observed in these cases. Bile duct ligation also induced ductal proliferation and fibrosis in all cases, but pericholangitis was not prominent. Retrograde cholangiograms in trinitrobenzenesulfonic acid rats showed distortion of the intra- and extrahepatic biliary tree. In conclusion, chronic cholangitis may be consistently induced in rats by a single intracholedochal administration of trinitrobenzenesulfonic acid.