We investigated the effect of two inhibitors of nitric oxide (NO) synthesis, N_w-nitro-l-arginine methyl ester (l-NAME) and aminoguanidine, on lung inflammation caused by intestinal ischemia/reperfusion in rats. Relative to the sham-operated rats, intestinal ischemia/reperfusion (ischemia: 45 min; reperfusion: 30 min, 2 and 4 h) induced neutrophil recruitment (increased myeloperoxidase activity) and increased microvascular permeability (Evans blue dye extravasation) in the lungs and increased tumor necrosis factor (TNF) levels in the serum (L-929 cytotoxicity assay). l-NAME given before the ischemia exacerbated neutrophil accumulation, plasma extravasation, serum TNF and caused death of the animals, which was prevented by concomitant injection of l-arginine. Lung and systemic effects of intestinal ischemia/reperfusion were not modified when l-NAME was given just before reperfusion. Treatment with aminoguanidine inhibited plasma extravasation without affecting the other parameters evaluated. Dexamethasone reduced all the parameters. Our results indicate that during intestinal ischemia/reperfusion both constitutive and inducible NO synthases are called to exert a differential modulatory effect on lung inflammation and that maintenance of adequate levels of NO during ischemia is essential for the animals survival.