Structural features of the endothelial integument of human arteries, not recorded in animals, have been revealed with scanning electron microscopy. Lipid streaks and atherosclerotic plaques areas were found to be covered with polymorphous endothelium, over 50% of the total surface being occupied by multinuclear endotheliocytes. These areas are characterized by increased absorption of low-density lipoproteins (LDL) due to non-specific binding. An analogous effect was observed in an endothelial culture from atherosclerotic aorta of an adult. Modified LDL are, on the contrary, absorbed in normal and atherosclerotic portions of the intima predominantly, or exclusively, through scavenger receptors. Human hepatocytes in the primary culture were found to contain receptors both for native and for modified LDL, the latter being absorbed 4 times as effectively as native LDL. It was shown that there are about 2500 binding sites of high-density lipoproteins on the surface of isolated human enterocytes. The cellular cultures obtained might be used in search for pharmacologic compounds correcting lipoprotein and cholesterol metabolism disorders.