Biliary lipid classes (bile acids, phospholipids, cholesterol) as well as individual biliary bile acids were measured in duodenal bile samples obtained before treatment from 284 white men and 264 white women participating in the National Cooperative Gallstone Study. The patients had radiolucent gallstones present in visualizing gallbladders. Calculated biliary cholesterol saturation was significantly higher in women (143 +/- 43, mean +/- SD, vs. 132 +/- 39 for men). Chenodeoxycholic acid was the major biliary bile acid in both sexes (40.0 +/- 9.9 in men; 38.8 +/- 9.3 in women, NS). Cholic acid was the second most common bile acid, constituting 32.9 +/- 8.8 in men and 31.8 +/- 8.9 in women (NS). When other demographic and clinical characteristics, including serum lipids, were related with biliary lipid composition, only percent ideal body weight correlated significantly. The partial correlation coefficient adjusted for percent ideal body weight indicated that the proportion of chenodeoxycholic acid correlated negatively with the mole fraction of cholesterol in bile in men, but not in women. Multiple regression analyses showed that bile saturation could not be predicted reliably from any clinical, chemical, or radiologic measurement in either sex. Published data for biliary lipid composition in individuals with biliary disease showed considerable overlap with the National Cooperative Gallstone Study data reported here, suggesting that cholesterol gallstone disease is not caused solely by increased biliary cholesterol saturation.