A new luminescent method was used to detect the reactive oxygen species in aqueous and vitreous humors and in homogenates of the lens and retina of laboratory rats. Superoxide-like activity per microgram protein increased in all tissues with weight of the rat, a good indicator of animal age. Superoxide dismutase, centrophenoxine, soluble vitamin E (D-alpha-Locopherol (polyethlyene glycol 1000) succinate, and N'-diphenyl-p-phenylenediamine (DPPD) reduced the luminescence. Catalase had no effect. These results are consistent with the detected species being superoxide-like.