Differences in lung heme oxygenase-1 (HO-1) regulation have been demonstrated in newborn (<12 h old) and adult (>2 month old) rats after exposure to hyperoxia. Contrary to adults, neonates do not demonstrate increased lung HO-1 induction nor transcription factor activator protein-1 (AP-1) binding in hyperoxia. Because AP-1 activation can be posttranslationally modified by oxidants or reductants, we investigated whether differences in lung glutathione (GSH) content account for the maturational differences in AP-1 activation and subsequent HO-1 gene regulation after hyperoxia. Neonatal rats were injected with either 1-buthionine-[S,R] sulfoximine (BSO), diamide, or selenite during the 72-h hyperoxic exposure. Lung GSH content, glutathione disulfide (GSSG) content, AP-1 binding, and HO-1 mRNA were evaluated. The ratios of GSSG to GSH were used to reflect the GSH redox state in the lungs. Changes in lung GSSG/GSH ratio did not alter AP-1 binding but did increase HO-1 mRNA in neonates. These data suggest that the neonatal lung is relatively resistant to AP-1 activation and HO-1 induction by GSH perturbation.