Lipid peroxidation was initiated with 5 mM ferric iron and aliquots of bovine or porcine retina, purified rod outer segments (ROS) and retinal pigment epithelium (RPE). After 30 min of oxidation, the lipid hydroperoxide content of the tissues increased approximately 4- to 8-fold over control levels with ROS showing the greatest change and RPE the lowest. Eight lipid and aqueous antioxidants from natural or synthetic sources and five flavonoids were evaluated for their ability to inhibit the reaction. Species differences were observed with regard to the fraction under study. Palm oil-derived vitamin E showed significant protection in bovine retina, ROS and RPE. In the porcine eye, the major defense was also afforded by vitamin E, but MCLA and other compounds such as EPC-K1 and U74500A were all quite active at 10(-5) M concentration. Of the flavonoids tested, partial protection in the bovine retina was found at 10(-5) M levels for epigallocatechin gallate (EGCg), quercetin, diosmetin and pycnogenol. When vitamin E and EGCg or quercetin were combined, the individual effect was enhanced. These results demonstrate the usefulness of an in vitro model system that can rapidly and accurately determine the capacity of antioxidants against lipid peroxidation.