ABSTRACT— A two-stage study was carried out to characterize the bile and plasma lipid composition in normolipidemic non-obese patients with and without cholesterol gallstones. The first stage involved 11 patients with cholesterol gallstones admitted for elective cholecystectomy and a control group of 16 patients without cholesterol gallstones undergoing elective laparotomy. Bile samples were obtained intraoperatively by aspiration from the gallbladder. The bile of all the gallstone patients was supersaturated with cholesterol and its nucleation time was much shorter than that of bile in the control group (2.5 days vs 22.5 days, respectively, P<0.001). The biliary fatty acid profile of phosphatidylcholine (PC) and free fatty acids (FFA) of gallstone patients was similar to that of the control group. C-22 fatty acids were found in a higher concentration in the FFA than in the PC fatty acids (P<0.05) in both groups of patients. Plasma triglyceride levels in the gallstone patients were significantly higher than those in the control group and the biliary cholesterol level correlated with that of plasma triglycerides. In the second stage of the study, plasma lipid profiles were obtained in two additional groups of patients, 20 patients with and 24 patients without cholesterol gallstones, for an in-depth characterization of the differences in plasma lipid profiles. The gallstone patients were found to have not only significantly higher concentrations of plasma triglycerides but increased cholesterol and phospholipid level as well. These differences were essentially due to a higher lipid content of the plasma VLDL fraction, similar to the pattern of patients with type IV hyperlipoproteinemia.