(±)17-HDHA is an autoxidation product of docosahexaenoic acid in vitro. It is also produced from incubations of DHA in rat liver, brain, and intestinal microsomes. 17(S)-HDHA could be produced by enzymatic oxidation of DHA using soybean lipoxygenase (LO) and is the putative product of mammalian 15-LOs. 17(S)-HDHA was shown to be an inhibitor of U-46619 -induced rabbit and rat aortic smooth muscle contraction with IC50 values of 4.9 and 7.2 μM, respectively. (±)17-HDHA is a potential marker of oxidative stress in brain and retina where DHA is an abundant polyunsaturated fatty acid.