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The effect of age on changes in glutathione (GSH)-shuttle enzyme activities in rat lungs following a 72-hr exposure to NO2 (14 ppm) or O3 (approximately 0.9 ppm) was investigated. Exposed animals survived and were in the adaptive recovery phase at sacrifice. Glucose-6-phosphate dehydrogenase, glutathione reductase, and glutathione peroxidase levels were significantly elevated in young adult or older rats (maternal nursing or normal) and, to a lesser degree, in weanlings. Enzyme levels of neonates remained essentially unchanged and their lungs showed minimal morphological injury. At 50 ppm NO2, neonates also exhibited significant elevations in all three enzyme levels. The comparative unresponsiveness of neonates to short-term, low-level exposure to NO2 or O3, together with other observations, indicate that the relative importance of the GSH-shuttle in protecting lungs against injury requires further investigation.