Postsepsis lung injury is a common clinical problem associated with significant morbidity and mortality. Leukotrienes (LTs) are important lipid mediators of infection and inflammation derived from the 5-lipoxygenase (5-LO) metabolism of arachidonate with the potential to contribute to lung damage after sepsis. To test the hypothesis that LTs are mediators of lung injury after sepsis, we assessed lung structure, inflammatory mediators, and mechanical changes after cecal ligation and puncture surgery in wild-type (WT) and 5-LO knockout (5-LO(-/-)) mice and in WT mice treated with a pharmacologic LT synthesis inhibitor (MK886) and LT receptor antagonists (CP105,696 and montelukast). Sixteen hours after surgery, WT animals exhibited severe lung injury (by histological analysis), substantial mechanical impairment (i.e., an increase in static lung elastance), an increase in neutrophil infiltration, and high levels of LTB4, cysteinyl-LTs (cys-LTs), prostaglandin E2, IL-1β, IL-6, IL-10, IL-17, KC (CXCL1), and monocyte chemotactic protein-1 (CCL2) in lung tissue and plasma. 5-LO(-/-) mice and WT mice treated with a pharmacologic 5-LO inhibitor were significantly protected from lung inflammation and injury. Selective antagonists for BLT1 or cys-LT1, the high-affinity receptors for LTB4 and cys-LTs, respectively, were insufficient to provide protection when used alone. These results point to an important role for 5-LO products in sepsis-induced lung injury and suggest that the use of 5-LO inhibitors may be of therapeutic benefit clinically.