To investigate the relationship between biliary mucin and ductular stone formation, mucin was isolated from hepatic bile using gel filtration on Sepharose CL-4B. The bile was obtained from 14 patients with stones in various sites of the biliary tract. The hexose content in the excluded fraction was significantly higher in patients with intrahepatic ductular stones (68.7 +/- 20.5 micrograms/mL; mean +/- s.d.) than in those with gall-bladder stones or extrahepatic ductular stones (23.8 +/- 8.1 micrograms/mL, 33.3 +/- 9.5 micrograms/mL; P less than 0.05), suggesting a higher concentration of mucin in the bile of patients with intrahepatic ductular stones. Ion-exchange chromatography on DEAE-Sephacel showed that most mucin from each material was negatively charged and electrophoretic studies indicated that it was composed mainly of high molecular weight (greater than 10(6)), sulfated glycoprotein. These results suggested that the mucin content of hepatic bile might have an important relation to the development of intrahepatic ductular stones.