The lipid composition of fasting gallbladder bile obtained under standardized conditions was determined in healthy controls and in patients with hyperlipoproteinemia without gallstones. Altogether 23 normolipidemic controls (10 males and 13 females) and 50 hyperlipidemic patients (31 type IIa, 7 type IIb, and 12 type IV) were studied; all were less than 15% overweight. The cholesterol saturation averaged 96 +/- 5% (mean +/- SEM) in the controls, and 10 of them had bile supersaturated with cholesterol. There was no difference between males and females. An increased saturation with age was seen in females. A normal biliary cholesterol saturation (102 +/- 3%) was found in patients with hyperlipoproteinemia type IIa; this was true also for the subgroup with established familial hypercholesterolemia. All patients with hyperlipoproteinemia type IIb and 10 of those with type IV had saturated bile (135 +/- 8% and 121 +/- 6%, respectively). The results suggest an association between certain forms of hyperlipoproteinemia and the development of supersaturated bile. Since fasting gallbladder bile supersaturated with cholesterol is considered to precede gallstone formation, the present results may explain previous findings of an increased prevalence of gallstone disease in patients with hypertriglyceridemia.