The treatment of severe lung disease often requires the use of high concentrations of oxygen coupled with the need for assisted ventilation, potentially exposing the pulmonary epithelium to both reactive oxygen species and non-physiologic cyclic stretch. While prolonged hyperoxia is known to cause increased cell injury, cyclic stretch may result in either cell proliferation or injury depending on the pattern and degree of exposure to mechanical deformation. How hyperoxia and cyclic stretch interact to affect the pulmonary epithelium in vitro has not been previously investigated. This study was done to explore the combined effects of cyclic stretch and hyperoxia on cell proliferation and viability using human alveolar epithelial A549 cells. Under room air conditions, cyclic stretch did not alter cell viability at any time point and increased cell number after 48 hrs compared to unstretched controls. Following exposure to prolonged hyperoxia, cell number and [³H] thymidine incorporation markedly decreased, while evidence of oxidative stress and non-apoptotic cell death increased. The combination of cyclic stretch with hyperoxia significantly mitigated the negative effects of prolonged hyperoxia alone on measures of cell proliferation and viability. In addition, cyclic stretch resulted in decreased levels of oxidative stress over time in hyperoxia exposed cells. Our results suggest that cyclic stretch, as applied in this study, can minimize the detrimental effects of hyperoxia on alveolar epithelial A549 cells.