It has been repeatedly shown that normal human gallbladder bile is commonly supersaturated wih cholesterol. It has been therefore suggested that the crucial step of the formation of cholesterol gallstones might be the nucleation and growth of cholesterol monohydrate crystals. Consequently this work was aimed at determining: 1) if cholesterol crystal formation is really a typical feature of gallbladder bile with cholesterol gallstones; 2) the influence of the degree of cholesterol saturation of bile on the formation of cholesterol crystals. Gallbladder bile from 89 patients (23 from patients with cholesterol gallstones, 7 from patients with non-cholesterol gallstones and 59 from patients free of gallstones) and hepatic bile from 17 previously cholecystectomized patients were studied. Four of these patients had cholesterol stones of the common bile duct. RESULTS (a) gallbladder bile: cholesterol crystals were present on immediate examination in 19 of the 23 bile samples with cholesterol stones, in 2 of the 7 bile samples with non-cholesterol stones and in 1 of the 59 bile samples without stones. Only 1 bile sample with cholesterol stone developed crystals. Cholesterol saturation of bile with or without crystals did not differ significantly; (b) hepatic bile: cholesterol crystals were detected on immediate examination in one of the 17 bile samples and subsequently appeared in one of the remaining samples. Cholesterol saturation of hepatic bile (2.10 +/- 0.43) was significantly higher (p less than 0.01) than that of gallbladder bile containing cholesterol stones (1.32 +/- 0.43).(ABSTRACT TRUNCATED AT 250 WORDS)