In vitro hepatic synthesis of lipids starting from (1-14C)acetate was investigated for 14 days in rats with biliary obstruction by ligation of the common bile duct using radio-thin-layer chromatography (radio-TLC). This study was correlated with a quantitative assay of the various hepatic lipids using TLC correlated with photodensitometry. Hepatic total lipid synthesis increased progressively with time. With concern to the single fractions, the major modifications were verified on the 3rd day with a decreased incorporation of the labelled acetate into the triglycerides. On the other hand, using photodensitometry, they demonstrated a percentage increase. These variations can be justified by the presence of a feedback mechanism. The syntheses of cholesterol and the other fractions were maximum during this period. Histologic examination revealed, especially on the 3rd day, a neoformation of biliary ductules and on the 14th day, a regression of these histological changes.