We hypothesize that the differential susceptibility to photic injury among different strains of rat retinas may depend on the levels of phospholipid hydroperoxide glutathione peroxidase (PHGPX) activity, one of the endogenous antioxidant enzymes in the retina. The retinas of four inbred strains of albino rat (Fischer, Wistar, Buffalo and Lewis) were analyzed for glutathione peroxidase activity using H2O2, cumene hydroperoxide, and phospholipid hydroperoxide as assay substrates. In all four strains of rat, PHGPX was observed only in the high salt extract of the retina, while peroxidases determined by H2O2 or cumene hydroperoxide were observed mainly in the low salt extract. PHGPX was highest (66.7 mU/mg) in the most light-resistant Fischer strain and lowest in the most light-sensitive Lewis strain (31.9 mU/mg), while the activity levels in the moderately light-sensitive Buffalo and Wistar strains were 46.6 and 38.5 mU/mg, respectively. In contrast, there was no significant difference in peroxidases determined by H2O2 or cumene hydroperoxide among the four strains. These observations suggested that, in rat retina, the membrane-associated PHGPX may have an important role in the defense against light-induced free radical damage.