This article discusses an overlooked subject, namely that serum lipemia affects the transfer of oxygen from the blood to the tissues. It discusses several mechanisms whereby lipemia limits oxygen diffusion. Observations of improved tissue oxygenation in atherosclerotic patients coincident with the clearing of lipemia by heparin are described. Conversely, the adverse effects of increased lipemia after fat meals upon tissue oxygen are noted. The contribution of hypoxia of the arterial wall to atherogenesis is outlined, and its adverse effects in the ischemic heart are listed.