Pulmonary vasorelaxation to endothelium-dependent and independent agonists is dysfunctional in endotoxin-induced acute lung injury. L-arginine is the precursor to endothelial production of nitric oxide (NO), suggesting that arginine and NO are intimately linked. We hypothesized that L-arginine would attenuate endotoxin-induced dysfunction of guanosine 3',5'-cyclic monophosphate-mediated pulmonary vasorelaxation.