Supersaturation of bile with cholesterol is generally considered the driving force of cholesterol precipitation. However, in most investigations the amount of cholesterol crystals is included in the calculation of the cholesterol saturation index (CSI). We therefore studied the solubility of cholesterol in crystal-free gallbladder bile from gallstone patients. Our results demonstrate significantly ( P <.05) higher CSIs (1.4 +/- 0.5 and 1.4 +/- 0.4 vs 1.1 +/- 0.4, mean +/- SD) in crystal-free gallbladder bile from 66 patients with cholesterol stones and 21 patients with mixed stones compared with those in 30 patients with pigment stones and a significant difference ( P <.001) in the amount of cholesterol in vesicles (19.2% +/- 13.7% and 14.3% +/- 11.6 % vs 4.2% +/- 5.9%) and of the crystal-observation time (COT; 1-21 days, median 2 days and 1-21 days, median 3 days, vs 3-21 days, median 21 days). We detected a positive correlation ( r =.24, P <.01) between the percentage of cholesterol in vesicles and the CSI and a negative correlation between COT and CSI ( r = -.23, P <.02 ) and COT and the percentage of cholesterol in vesicles ( r = -.52, P <.001 ). However, in 14 of 30 gallbladder-bile specimens from patients with pigment stones but in just 5 of 21 specimens from patients with mixed stones patients and 12 of 66 specimens from patients with cholesterol stones, the distribution of cholesterol in different phases (mixed micelles, vesicles, and crystals) was within the limits of solubility determined in previous studies of model bile. Therefore, in addition to the relative composition of biliary lipids, nonlipid components exert considerable influence on the solubility of cholesterol in the gallbladder bile of gallstone patients.