Sweden has one of the highest incidences of gallstone disease in the Western world. It is therefore important to characterize the mechanisms responsible for the formation of cholesterol gallstones in this population. In the present study, we have determined the kinetics of the two primary bile acids, cholic acid and chenodeoxycholic acid, and the hepatic secretion rates of the biliary lipids in 21 normolipidemic, nonobese gallstone patients (13 with functioning and 8 with nonfunctioning gallbladder) and in 23 healthy controls. The cholesterol saturation of fasting gallbladder bile averaged 110% in the gallstone patients with functioning gallbladder and 82% in the controls. The pool sizes of cholic acid and chenodeoxycholic acid were reduced by about 40% in the two groups of gallstone patients, whereas the rates of synthesis were close to normal. The fractional catabolic rate of both bile acids was increased in both groups of gallstone patients. The gallstone patients with functioning gallbladder had an increased (about 50%) cholesterol secretion but normal bile acid and phospholipid secretion rates. In the gallstone patients with nonfunctioning gallbladder the secretion rates of biliary lipids were not significantly different from those of the controls. The ratio between cholesterol and bile acids was about 50% higher in the gallstone patients with functioning gallbladder than in the controls or in those with nonfunctioning gallbladder. The results indicate that the hepatic secretion of cholesterol is an important determinant for the development of saturated gallbladder bile in Swedish gallstone patients.