In the retina, as well as in other organs, inflammation-mediated membrane lipid peroxidation is regarded as the major source of unsaturated fatty acid hydroperoxides. It is generally accepted that inflammatory infiltrates, such as polymorphonuclear leukocytes and macropahges, simultaneously generate superoxide and nitric oxide (NO) (1 ). Although both radicals display low chemical reactivity, their combination product, peroxynitrite, is a potent oxidant capable of oxidizing cellular macromolecules, including membrane lipids (2 ). Photoreceptor membranes in the retina contain an unusually high concentration of docosahexaenoic acid (22:6, omega 3), amounting to nearly 50% of the total fatty acid pool (3 ). By virtue of its structure, 22:6 is particularly susceptible to lipid peroxidation induced by peroxynitrite (2 ,2 ).Peroxidation of photoreceptor membranes in the retina has been recognized as a key component in various types of photoreceptor degeneration and pathogenesis (5 ). Interest in the pathological consequences of photoreceptor membrane lipid peroxidation has led to the development of several analytical approaches designed to detect peroxidized lipids in the retina.