Results of attempts to ameliorate hyperoxic pulmonary injury using novel systems for delivery of antioxidant enzymes are reviewed. Intratracheal insufflation of either liposome encapsulated superoxide dismutase or encapsulated catalase increased levels of enzyme activities in rat lung homogenates and prevented lethal effects of an atmosphere of oxygen. Intact erythrocytes placed in the tracheobronchial tree of rats also dramatically improved survival in hyperoxia. Recyclable glutathione appeared to be the constituent of erythrocytes, which was responsible for the protection. In rabbits, erythrocytes also protected from oxidant-mediated ischemic-reoxygenation lung injury. These studies suggest a possible role for erythrocytes as biologic packets of antioxidant enzymes.