INTRODUCTIONHelicobacter pylori is known to play a signiŸcant aetiopathogenetic role in peptic ulcer disease. Triple therapy using colloidal bismuth subcitrate in combination with amoxycillin and metronidazole has been shown not only to heal peptic ulcers but also to prevent their recurrence. 1, 2 In a previous study, we demonstrated that amoxycillin, in addition to its antimicrobial action, imparted gastric cytoprotection through the action of prostaglandins in the gastric mucosa. 3 The present study aimed to determine whether metronidazole, one of the most commonly used antimicrobials for anti-Helicobacter pylori therapy, has similar organoprotective properties. In order to test this hypothesis, both ethanol and indomethacin ulcer models were employed in the rats. Evaluation of gastric mucosal mucus, prostaglandin E 2 (PGE 2 ) content, blood¯ow and potential difference across the mucosa were performed because these parameters have been shown to be the key factors in the maintenance of gastric mucosal integrity. 4±8 Furthermore, the effects of metronidazole on the vascular and glandular integrity of the stomachs of SUMMARY Background: The gastroprotective action of metronidazole, an antimicrobial used in the therapy against Helicobacter pylori infection, is unclear. Thus, the aim of the present investigation was to study the organoprotective action and antiulcer mechanisms of this drug in rodents. Methods and results: Metronidazole (10 mg/kg), given either per os or intraperitoneally, 30 min beforehand, reduced ethanol (40%, 10 mL/kg, p.o.)-induced gastric mucosal damage in male rats. Likewise, oral administration of metronidazole dose-dependently attenuated the indomethacin (30 mg/kg, p.o.)-induced gastric lesion formation and the concurrent depletion of mucosal mucus. However, metronidazole did not affect the basal mucosal prostaglandin E 2 content. In an ex vivo gastric chamber preparation, 40% ethanol incubation markedly lowered transmucosal potential