Nitric oxide appears to play an important role in maintaining gastric mucosal integrity. This study aimed to investigate whether a nitric oxide donor (sodium nitroprusside) or stimulation of endogenous nitric oxide synthesis (with acetylcholine) protects against gastric ischemia-reperfusion injury. Rats were subjected to 30 min of ischemia followed by 15 min of reperfusion. Injury was assessed by quantitative histology. Intravenous sodium nitroprusside (50-75 micrograms/kg) or acetylcholine (10-25 micrograms/kg), immediately before reperfusion, significantly reduced the percentage of mucosal injury compared with controls. Inhibition of nitric oxide synthesis by topical application of 12.5 mg/kg NG-methyl-L-arginine before acetylcholine treatment, abolished the effects of acetylcholine. The protective effects of acetylcholine and sodium nitroprusside did not appear to be related to local vasodilation since neither drug improved gastric blood flow and infusion of a non-nitric oxide vasodilator (papaverine, 1 mg/kg), had no protective effect on reperfusion injury. Sodium nitroprusside (50 micrograms/kg) and acetylcholine (25 micrograms/kg) significantly reduced polymorphonuclear leukocyte infiltration and extravasation into the mucosa compared with controls. NG-Methyl-L-arginine pretreatment before acetylcholine abolished these effects. We conclude that nitric oxide generators significantly reduce mucosal injury following ischemia-reperfusion and that this may occur via a reduction in polymorphonuclear leukocyte infiltration into the mucosa.