Linolein hydroperoxides are a mixture of 132 possible isomers of mono-, di-, and tri-hydroperoxides produced from the autoxidation of trilinolein. Autoxidation of linoleic acid containing triglycerides (for example, trilinolein) in vivo could result in the formation of these hydroperoxides. Unlike the free fatty acid hydroperoxides of linoleic acid (for example, 13-HpODE), linolein hydroperoxides are not readily reduced in human plasma in vitro. Circulating linolein hydroperoxides could contribute to the pathophysiology of atherosclerosis.