The effect of a cholesterol-enriched diet was studied in nine healthy volunteers with special emphasis to the changes which occurred in the triglyceride-rich lipoproteins (d<1.019 g/ml). Compared to the habitual diet, a moderately increased intake of cholesterol (from 300–900 mg/day) resulted in changes of the lipid composition and in a decrease of the apoprotein bands apo B-100, C and E of the d<1.019 g/ml fraction by 25–30%. On the average, the intensity of the apo B-48 band increased. The most consistent was a decrease of cholesterol and triglycerides in the d<1.019 g/ml fraction binding to heparin-Sepharose considered to represent remnants of very low-density lipoproteins. Low-density lipoprotein cholesterol increased by 0.2 mmol/l (ns). However, three subjects with relatively low concentrations of lipids and apoproteins in the d<1.019 g/ml fraction showed a hyperresponse of LDL-cholesterol by more than 0.5 mmol/l. In these subjects the intensity of the B-48 band did not increase on the cholesterol-enriched diet. The results suggest, that the rise in LDL-cholesterol caused by dietary cholesterol is mediated by an enhanced uptake of chylomicron- and VLDL-remnants by the liver, followed by a secondary down-regulation of the LDL-receptors.