Proper engagement of leukocyte and endothelial cell selectins with their counterreceptors is an initial step in neutrophil trafficking to sites of inflammation. Certain fucosylated carbohydrate determinants such as sialyl Lewis-x are proposed to act as these counterreceptors. We studied the effects of a synthetic sialyl Lewis-x analog, CY-1503, on the course of hemodynamic derangements and acute lung injury during experimental gram-negative sepsis. Anesthetized ventilated swine were made septic with an infusion of live Pseudomonas aeruginosa. A treatment group received an initial bolus of CY-1503 (60 mg/kg) before sepsis, followed by continuous infusion of CY-1503 (15 mg.kg-1.h-1). Treatment with CY-1503 did not prevent the development of pulmonary hypertension, systemic hypotension, decline in cardiac output, or severe neutropenia. However, CY-1503 significantly attenuated lung injury, demonstrated by decreased bronchoalveolar lavage protein content and neutrophil influx, lowered lung myeloperoxidase activity, and improved arterial oxygenation. Neutrophils from septic and CY-1503 animals showed significant activation, reflected by upregulated CD18 expression and priming for oxidant burst compared with control animals. This study suggests blockade of selectin interactions as a potential therapeutic intervention in sepsis-induced lung injury.