The effect of endoscopic sphincterotomy on bile acid composition and cholesterol saturation of bile has been studied in cholecystectomized patients. Individual bile acids and biliary lipids were measured in hepatic bile of 13 cholecystectomized females aged 56.8 +/- 16.6 years more than 9 months (mean 16.7 +/- 8.8 months) after sphincterotomy and of 12 cholecystectomized females aged 59.3 +/- 11.5 years who served as controls. The sphincterotomy group exhibited a significantly (p less than 0.01) higher percentage of chenodeoxycholic acid in bile--39.2 +/- (SD) 7.7%--than the controls with cholecystectomy only (29.1 +/- 7.4%), but showed no differences in the proportion of cholic acid (32.4 +/- 6.2 vs. 33.6 +/- 7.8%). The percentages of the secondary bile acids, deoxycholic acid (25.0 +/- 8.8 vs. 32.3 +/- 8.3%), and lithocholic acid (1.7 +/- 0.8 vs. 2.6 +/- 2.3%) were lower, but these differences were not statistically significant. The biliary lipid composition in the sphincterotomy group was not different from that in the controls, resulting in a similar cholesterol saturation index in both groups (1.87 +/- 0.60 vs. 2.02 +/- 0.60 according to Carey and Small; 1.45 +/- 0.32 vs. 1.55 +/- 0.32 according to Hegardt and Dam). These findings do not demonstrate any alterations of the bile composition after sphincterotomy which may be expected to have undesirable effects on the biliary and/or gastrointestinal system.