This presentation deals only with selected early manifestations of arterial pathology, i.e., lipid accumulation, and leans more heavily on my own work than is warranted by its importance. I shall, however, synthesize our findings with those of others in support of the view that arterial lipid accumulates as the result not only of abnormally high concentrations of low-density lipoproteins (LDL) in the blood plasma, but also a consequence of the normal process of lipid absorption and transport. This normal process may be innocuous in persons who ingest low-fat diets, but is probably pathogenic in those who consume a diet rich in fat and cholesterol.