This study was carried out primarily to determine whether the feeding of lecithin (polyenylphosphatidylcholine) has systemic effects on metabolism of cholesterol and triglycerides in patients with endogenous hypertriglyceridemia (type 4 hyperlipoproteinemia). Ten patients were studied during control periods and lecithin feeding. In the former period, 7 g of safflower oil were added to the diet to balance the addition of 10 g of lecithin in the latter period. Lecithin feeding had no influence on levels of plasma cholesterol and triglycerides, or lipoprotein-cholesterol, transport of VLDL-triglycerides, or total steroid balance. However, lecithin feeding did significantly increase the molar percent of bile acids and decrease the molar percent lecithin in gallbladder bile suggesting that it has a systemic effect. In addition, it had a small but significant inhibitory effect on intestinal absorption of cholesterol.