The volume density of bile ducts in adult normal liver has been analyzed in order to provide stereometric parameters to which refer on performing quantitative evaluations of bile duct loss in acquired liver diseases. Five livers were studied by applying a semi-automatic image analysis system (ASM 68K Leitz) to histological sections. No significant differences (P > 0.10) were found for all measures and the following values were derived from the pooled data: (1) mean % volume of bile ducts in liver = 0.318 +/- 0.171; (2) mean % volume of portal tracts in liver = 4.351 +/- 2.860; (3) mean % volume of bile ducts in portal tracts = 6.567 +/- 3.813. The parallelism of bile duct to arterial components of portal tracts was also investigated and expressed as the ratio of their respective volume fractions (mean ratio = 1.72). The validity of the obtained parameters was tested by comparing them with values determined in five cases of primary biliary cirrhosis (PBC). All PBC cases showed a marked decrease in both bile duct % volume in liver (ranging between 0.028 and 0.057) and bile duct % volume in portal tracts (ranging between 0.673 and 0.914), as well as inversion of the bile duct to artery volume ratio in portal tracts (ranging between 0.246 and 0.437).