Chloroquine (1, 5 and 10 mg/kg), given in acute and in chronic (7 and 15 days) treatment schedules, caused characteristic alterations in the lysosomal enzyme system, antioxidant enzymes, NADPH-induced lipid peroxidation, and glutathione content in the retina of the rat. One-half hour and four hours after chloroquine administration, increased free activities of lysosomal enzymes and NADPH-induced lipid peroxidation were observed, associated with a decrease in tissue glutathione content. In contrast to the acute effect, chloroquine, given in 7- and 15-day treatment schedules, had no significant effect on the lysosomal enzyme system, while at the same time a normalization or a decrease in NADPH-induced lipid peroxidation, associated with a significant increase in tissue glutathione content, was noted. Catalase and peroxidase activities were decreased after both the acute and the daily treatment schedules. Superoxide dismutase activity, although increased in the high dose acute study, appeared otherwise little affected by chloroquine treatment. © 1983.