An important function of endothelium is to release PGI2, a prostaglandin produced from arachidonic acid that prevents platelet aggregation and causes arterial relaxation. Small amounts of other eicosanoids also are produced, but their role in endothelial function has not been elucidated. Much of the arachidonic acid present in the endothelium is obtained preformed from the plasma, either as FFA or from lipoproteins. Arachidonic acid is efficiently incorporated into endothelial lipids even when only relatively small amounts are available. In response to agonists, arachidonic acid is rapidly released from the endothelial phospholipids and converted to eicosanoids. Small amounts of eicosanoids also are continuously formed due to exposure of the endothelium to free fatty acid and lipoproteins containing arachidonic acid, without the need for any additional stimulus. Although the role of plasma lipid abnormalities has not been systematically investigated, there presently is little indication that hyperlipidemia interferes with endothelial arachidonic acid metabolism or the capacity of the endothelium to produce eicosanoids.