The objective of this study was to investigate possible pathogenetic factors for cholesterolosis. Liver tissue, gallbladder mucosa, and gallbladder bile were collected in patients with cholesterol gallstones (GS) (14 patients with and 14 patients without cholesterolosis) and gallstone-free (GSF) subjects (11 with and 21 without cholesterolosis) undergoing cholecystectomy. In cholesterolosis, the gallbladder mucosa was characterized by a fivefold increase in esterified cholesterol and normal content of free cholesterol. The hepatic levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, governing cholesterol synthesis, and acyl coenzyme A: acyltransferase activity, catalyzing the esterification of cholesterol, were similar in patients with and without cholesterolosis. Also in the gallbladder mucosa, the 3hydroxy-3-methylglutaryl coenzyme A reductase activity was similar in patients with and without cholesterolosis. The acyl coenzyme A: acyltransferase activity of the gallbladder mucosa was increased in the GSF subjects with cholesterolosis. The nucleation time of gallbladder bile was shorter in the GSF subjects with cholesterolosis compared with the time of those without cholesterolosis. Occurrence of cholesterol crystals, lipid composition, and cholesterol saturation of gallbladder bile were not significantly influenced by the absence or presence of cholesterolosis. The study has confirmed that cholesterolosis is associated with a several-fold increased level of esteritied cholesterol. The data suggest that patients with cholesterolosis have normal hepatic cholesterol formation and esterification. The local synthesis of cholesterol in the gallbladder mucosa seems to be normal. A positive correlation was obtained between the cholesterol saturation of bile and the content of esterified cholesterol in the gallbladder mucosa in the whole series of patients. However, because cholesterolosis may occur in both GSF subjects and patients with