Acute lung injury, whose most severe expression is Respiratory Distress Syndrome, was described 40 years ago. Despite all research in this field, mortality rate still remains around 35%. In this study we used a model of acute lung injury with paraquat, an herbicide that causes alveolar instability through destruction of surfactant, to obtain pressure-volume curves of lungs in open-chest rats. The objectives were to study acute lung injury through measurements of lung elastance during inspiratory and expiratory maneuvers. We observed a rise in elastance during the initial part of the inspiratory maneuver (0-5mL approx.) in animals exposed to paraquat possibly due to increased alveolar collapse. We suppose that alveolar recruitment is responsible for the absence of significant elastance changes in other phases of the inspiratory maneuver.