9(R)-HODE is one of several monohydroxylated products of linoleic acid. All known mammalian lipoxygenases appear to catalyze the oxygenation of arachidonic and linoleic acid to give products having strictly the (S) configuration at the site of oxygen insertion. However, both human umbilical vein endothelial cells and bovine aorta endothelial cells have been shown to produce 9(R)-HODE when incubated with linoleic acid. The physiological function of 9(R)-HODE and the enzyme that catalyzes its formation have not been determined.