Highly polyunsaturated phosphatidylcholine (PC) was orally administered to patients with familial hypercholesterolemia and normal controls. Plasma lipid and lipoprotein composition as well as fecal sterol excretion and bile lipid composition were analyzed. Two dietary regimens were given, containing similar amounts of calories, cholesterol and polyunsaturated fatty acids in order to evaluate the specific effect of phosphorylcholine. No change in plasma lipid or lipoprotein concentration was observed. However, fecal sterol excretion was substantially increased in all subjects when PC was added to the diet. Bile acids, phospholipid and cholesterol content in bile did not vary.