The antioxidant enzymes catalase and superoxide dismutase have integral roles in controlling reactive oxygen radicals that can harm cells. In the present study, we quantitated catalase activity in retinal pigment epithelium, retina, iris, and vitreous from human donors. To our knowledge, our results represent the first quantitation of catalase activity in human retinal pigment epithelium and show six-fold greater catalase activity in retinal pigment epithelium than in other ocular tissues analyzed (P less than .0001). To investigate whether aging or macular degeneration affects retinal pigment epithelium catalase or superoxide dismutase activities, we measured enzyme levels in retinal pigment epithelium from donors 50 to 90 years of age with and without evidence of macular degeneration. Superoxide dismutase activity showed no significant correlations with aging or macular degeneration, while catalase activity decreased with age (P less than .02) and macular degeneration (P less than .05) in both macular and peripheral retinal pigment epithelium.