Plasmatic levels of low density lipoproteins (LDL) are regulated by the receptor pathway and most LDL receptor are located in the liver. A receptor defect due to genetic mutations of the LDL receptor gene is the cause of familial hypercholesterolemia (F. H.), a disease characterized by high cholesterol levels and premature atherosclerosis. Injection of autologous radiolabelled LDL, followed by hepatic scintiscanning, can be used to obtain "in vivo" quantification of hepatic receptor activity, both in normal and hypercholesterolemic patients. In this study we observed no hepatic increase of radioactivity in patients affected by F. H., confirming the liver receptor defect. Scintigraphy is a non-invasive technique which can be used to diagnose this disease and to monitor the efficacy of hypolipidemic therapy.