 Respiratory failure due to ALIARDS remains a major health problem, despite significant progress in intensive care unit care and ventilator management. ALIARDS is characterized by unacceptably high mortality despite enormous expenditure of health care resources. Survivors face long-term consequences that may affect their quality of life. New therapies are needed to improve early survival and to decrease long-term sequelae of this syndrome. GM-CSF is a naturally occurring cytokine that is present in the normal lung, with important roles in pulmonary homeostasis. GM-CSF is essential for normal maturation and function of alveolar macrophages resident inflammatory cells that are responsible for initial defense against pneumonia. Alveolar epithelial cells line the gas exchange surface of the lung. Acute lung injury and subsequent abnormal healing is linked to delayed repair of damage to the epithelium following initial injury. This can then lead to pulmonary fibrosis. GM-CSF has potent effects on alveolar epithelial cells, promoting proliferation and limiting epithelial cell death. Thus, GM-CSF has a distinctive combination of activities that make it an excellent candidate for a therapeutic intervention in ALIARDS. Preliminary studies for this project demonstrate that GM-CSF can protect experimental animals against acute lung injury, can decrease susceptibility to pneumonia, and is protective against pulmonary fibrosis following acute lung injury. There is extensive experience with the administration of recombinant human GM-CSF to human patients this biological is approved by the FDA and has been well-tolerated in trials involving critically ill patients. This project is based on the hypothesis that administration of GM-CSF will improve clinical outcomes for patients with ALIARDS. 