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Albino rats were born and raised to 12 weeks of age in 12L:12D light regimes of 5, 300 or 800 lx. Upon killing, the activities of the following glutathione enzymes were measured in the neuroretina: (1) glutathione peroxidase; (2) glutathione-S-transferase; and (3) glutathione reductase. Also measured were vitamin E, ascorbic acid, and the levels of oxidized and reduced glutathione. Animals raised in 800-lx cyclic light have a significant increase in the retinal activities of the three glutathione enzymes over activities measured in animals raised in the two dimmer regimes. The retinal level of vitamin E, measured per nmol of lipid phosphorus, is directly and significantly correlated with rearing illuminance (P less than 0.05). The same is true of retinal ascorbic acid, which shows a 30% increase in the 800-lx-reared rats over the level of those raised in the intermediate light regime (300 lx). Some of the animals from each group were exposed to 2000 lx for 24 hr to determine if correlations existed between the levels of retinal antioxidants listed above and susceptibility to light damage. Animals raised in 5-lx cyclic light lost almost all of their photoreceptors as a result of the exposure. Rats raised in 300-lx cyclic light lost a small but significant number (ca. 20%), while those raised in 800 lx sustained no light damage. Electroretinographic evaluation supports these morphometrical findings.