(±)7-HDHA is an autoxidation product of 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 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 PUFA.