The protective effect of T-593 ((+/-)-(E)-1-[2-hydroxy-2-(4-hydroxyphenyl)ethyl]-3'-[2-[[[5-(methylamino) methyl-2-furyl]methyl]thio]ethyl]-2"-(methylsulfonyl)guanidine, CAS 140695-21-2), a new histamine H2-receptor antagonist, was investigated in rats with acute gastric mucosal injury. An ischemic injury followed by reperfusion was produced by applying a small vascular clamp to the celiac artery for 30 min and then removing it for 60 min. T-593 significantly reduced the area of the lesion in the stomach in a dose-dependent manner, and doses of 0.3 and 3.0 mg/kg inhibited the increase of lipid peroxides in the gastric mucosa after ischemia-reperfusion. A spin-trapping method using 5,5-dimethyl-1-pyrroline-N-oxide showed that T-593 scavenged hydroxyl radicals generated by the hydrogen peroxide-ferrous iron sulfate system. T-593 also significantly inhibited the increase of lipid peroxides induced by free-radical initiators in gastric mucosal homogenates. Thus, the protective effect of T-593 against acute gastric mucosal injury induced by ischemia and followed by reperfusion may result, in part, from its antioxidant properties.