The effects of acute (3 h), repeated acute (3 exposures each of 3 h) and chronic (72 h) normobaric hyperoxic exposure in budgerigars (Melopsittacus undulatus) were evaluated by monitoring the effects on pulmonary enzymic antioxidants, and indicators of lipid peroxidation. All durations of oxygen exposure resulted in significant respiratory alkalosis and elevated pulmonary and blood glutathione peroxidase concentrations. The concentrations of other pulmonary enzymic antioxidants including glutathione reductase and superoxide dismutase were not significantly altered by oxygen exposure. Pulmonary concentrations of the lipid peroxidation markers malonaldehyde and 4-hydroxyalkenal were not significantly elevated following oxygen exposure. Plasma concentrations of 8-epi isoprostane F(2alpha) were significantly elevated following both acute and repeated acute exposure. The results indicate that in budgerigars, both acute and chronic oxygen exposure can result in significant alteration in respiratory function and increased production of reactive oxygen species.