Addition of ionic and nonionic water-soluble polymers to pulmonary surfactants in the presence of inactivating substances prevents surfactant inactivation in vitro and improves lung function in several models of lung injury. However, a recent report found opposite effects when surfactant plus polyethylene glycol (PEG) was used to treat lung injury caused by saline lung lavage. Therefore, we examined the reasons why the polymer effect is less evident in the saline lung lavage lung injury model. We treated rats with lavage lung injury with a commercial lung surfactant extract derived from bovine lung (Survanta) with or without addition of PEG. Groups treated with Survanta ϩ PEG had significantly higher static post mortem lung volumes than groups treated with Survanta. However, groups treated with Survanta ϩ PEG had more tracheal fluid and no significant benefit in arterial oxygenation compared with the group treated with Survanta, despite our use of measures to reduce pulmonary edema. Measurements after intravascular injections of 125 I-labeled albumin confirmed that addition of PEG increased extravascular lung water and that this effect is mitigated by furosemide. We conclude that surfactant ϩ PEG mixtures are less effective in lavage injury than in other forms of lung injury because of increased extravascular lung water. ALI results from a variety of insults as diverse as meconium aspiration in newborns, hydrochloric acid reflux, sepsis, and ventilator trauma. In turn, injury predisposes the patient to acute (or adult) respiratory distress syndrome (ARDS) (1-4). Pulmonary surfactant replacement, now a mainstay in the treatment of respiratory distress syndrome in premature infants, has not enjoyed comparable success in treating ARDS (5-7). Inadequate dosage or distribution, and inactivation of surfactant have been postulated for its poor performance in treating these injuries (8 -11).Multiple reports indicate improved surfactant function when polymers such as dextrans, PEG, and hyaluronan are added to surfactant preparations in vitro (12-15). Animals with ALI have improved lung function when treated with surfactant polymer mixtures versus surfactant alone. found that adult rats receiving surfactant ϩ PEG, dextran, or hyaluronan mixtures have better gas exchange, pulmonary mechanics, and histologic appearance of the lungs when compared with rats treated with Survanta (beractant) alone after HCl-, meconium-, and endotoxin-induced lung injuries. Kobayashi et al. (19,20) have shown that addition of dextran to surfactant improves responses in two additional lung injury models (albumin inhibition in immature rabbits and acid milk aspiration in rats).The specific model used to induce ALI, however, may affect treatment responses to surfactant and surfactant ϩ PEG, as different models of lung injury produce different alveolar environments. A lavage model of lung injury, for example, removes variable amounts of alveolar surfactant (21), whereas a meconium model of lung injury inactivates but does not remove surfactant. P...