The adult respiratory distress syndrome is an acute clinical illness characterized by noncardiogenic pulmonary edema and refractory hypoxemia. Injury to the alveolar-capillary barrier and lung inflammation lead to intrapulmonary shunting of blood, surfactant depletion, and pulmonary vascular obstruction. Numerous mediators contribute to the pathologic response. Conventional therapy includes treating underlying causes and positive pressure mechanical ventilation. Concern about pressure-induced lung injury had led to new strategies to accomplish adequate gas exchange. Novel therapeutic interventions have included extracorporeal support techniques, use of compounds designed to neutralize proinflammatory cytokines, and administration of surfactants, but these efforts have not definitely affected mortality in randomized trials. Potent antioxidant agents have shown promise in animal models of acute lung injury, but human studies are lacking. Inhaled nitric oxide appears to have temporary effects on pulmonary artery pressure and on ventilation or perfusion relationships, but longer-term efficacy and safety in patients suffering from adult respiratory distress syndrome is unknown and awaits results of ongoing clinical trials.