Thirty-nine patients with cholelithiasis were prospectively studied to evaluate the qualitative and quantitative differences between duodenal bile and gallbladder bile. Duodenal bile obtained before cholecystectomy by nasoduodenal intubation and ceruletide injection was qualitatively similar to gallbladder bile obtained during surgery. Microscopic cholesterol crystals as an indicator of cholesterol gallstones (n = 35) could be detected in 31 (89%) and 35 (100%; p = NS), respectively. Moreover, there was no difference in the molar percentage of three biliary lipids and the mean cholesterol saturation index (1.54 +/- 0.72 and 1.74 +/- 0.42; p = NS) of the two sources of bile. Duodenal bile was, however, dilute as compared with gallbladder bile, as evidenced by lower cholesterol crystal counts (167 +/- 247 versus 705 +/- 978; p < 0.01), lower total lipid concentration (5.8 +/- 2.7 versus 11.1 +/- 5.6 g/dl; p < 0.001), and lower concentrations (in mmol/l) of the three bile lipids--that is, total bile acids, phospholipids and cholesterol (p < 0.001). Good concentrated bile (total lipid concentration > or = 5 g/dl) could be obtained in 74% of duodenal bile samples, compared with 90% of gallbladder bile (p = NS). Our study shows that, although duodenal bile is dilute as compared with gallbladder bile, it is qualitatively similar to gallbladder bile and, because of the ease and safety of its collection, can be used to study serial alterations in biliary composition in individual subjects.