(±)7-HDHA is an autoxidation product of docosahexaenoic acid (DHA) in vitro. It is also produced from incubations of DHA in rat liver, brain, and intestinal microsomes. Enzymatic transformation of DHA by RBL-1 cells and human neutrophils also produces 7-HDHA. However, the enzymatic product is most likely the S-isomer. (±)7-HDHA is a potential marker of oxidative stress in brain and retina where DHA is an abundant polyunsaturated fatty acid.