gamma-Glutamyl transferase (GGT) regulates glutathione metabolism and cysteine supply. GGT inactivation in GGT(enu1) mice limits cysteine availability causing cellular glutathione deficiency. In lung, the resultant oxidant burden is associated with increased nitric oxide (NO) production, yet GGT(enu1) mice still exhibit higher mortality in hyperoxia. We hypothesized that NO metabolism is altered under severe oxidant stress and contributes to lung cellular injury and death. We compared lung injury, NO synthase (NOS) expression, nitrate/nitrite production, nitroso product formation, peroxynitrite accumulation, and cell death in wild-type and GGT(enu1) mice in normoxia and hyperoxia. The role of NOS activity in cell death was determined by NOS inhibition. Exposure of wild-type mice to hyperoxia caused increased lung injury, altered NO metabolism, and induction of cell death compared with normoxia, which was attenuated by NOS inhibition. Each of these lung injury indices were magnified in hyperoxia-exposed GGT(enu1) mice except nitrosation, which showed a diminished decrease compared with wild-type mice. NOS inhibition attenuated cell death only slightly, likely due to further exacerbation of oxidant stress. Taken together, these data suggest that apoptosis in hyperoxia is partially NO-dependent and reiterate the importance of cellular glutathione in lung antioxidant defense. Therefore, reduced denitrosylation of proteins, possibly resulting in impaired cellular repair, and excessive apoptotic cell death likely contribute to increased lung injury and mortality of GGT(enu1) mice in hyperoxia.