PERSPECTIVES AND SUMMARY 898 LDL, THE MAJOR CHOLESTEROL-CARRYING LIPOPROTEIN OF HUMAN PLASMA . 901 Structure of Plasma LDL .. ... .... 901 Origin of Plasma LDL 902 Catabolism of Plasma LDL 902 THE LDL PATHWAY IN HUMAN FIBROBLASTS ..... ...... 903 The LDL Receptor 903 Endocytosis of Receptor-bound LDL .... 908 Lysosomal Hydrolysis of LDL-Protein and LDL-Cholesteryl Esters 910 Regulation of Cholesterol Synthesis and Cholesteryl Ester Formation .... .. 911 REGULATION OF THE LDL RECEPTOR . 912 MUTATIONS AFFECTING THE LDL PATHWAy 915 THE LDL PATHWAY IN CULTURED HUMAN LYMPHOID CELLS AND AORTIC SMOOTH MUSCLE CELLS ... . ..... ........ .... 918 THE LDL PATHWAY IN HUMAN CELLS IN VIVO 919 IMPLICATIONS OF THE LDL PATHWAY FOR NORMAL HUMAN PHYSIOLOGY AND THE PATHOGENESIS OF ATHEROSCLEROSIS ........ ....... 923