Although histologic studies of mucin distribution in the peribiliary glands have been conducted, a quantitative study of mucin content in intrahepatic bile ducts has yet to be reported. In an attempt to evaluate the mucin content in stone-containing intrahepatic bile ducts, we conducted a study on 25 surgically resected livers with hepatolithiasis. Specimens from 10 livers without stones served as controls. All specimens were fixed in 10% formalin and sectioned for periodic acid Schiffalcian blue double-stain (PAS-AB; pH 2.5) to evaluate the epithelial mucin content of the intrahepatic bile ducts. The PAS-AB positive area and the total epithelial area were measured with a computerized image analyzer and the PAS-AB index was calculated as the proportion of the PAS-AB positive to the total epithelial area. The histochemical study showed that epithelial cells in both the intramural glands and extramural glands of stone-containing intrahepatic bile ducts stained heavily and homogeneously with PAS-AB, while those of controls stained weakly. The PAS-AB indexes in stone-containing intrahepatic bile ducts were 51.8 +/- 15.88% for mucous cells of intramural glands, 52.86 +/- 9.85% for mucous cells of extramural glands, and 77.29 +/- 21.59% for serous cells of extramural glands. These values were all significantly higher than those of control specimens. However, the PAS-AB index of the epithelial lining in both hepatolithiasis and control specimens were similarly low, indicating the epithelial lining does not secrete much mucous glycoprotein. The results of this study led us to conclude that stone-containing intrahepatic bile ducts contain an abundant amount of mucous glycoprotein, and mucin is secreted from the peribiliary glands, not from the epithelial lining of the bile ducts.