The effect of the radical removing agents, allopurinol and dimethyl sulphoxide (DMSO), on the healing rate of ethanol (1 ml of 40% solution) induced gastric mucosal injury was studied in the rat. One millilitre of 1 2 or 5 % allopurinol or DMSO were instilled into the stomach 1 24 and 48 h after giving ethanol by gavage. One hour after administration of ethanol, gastric mucosal injury was produced in all animals (20.4 ± 1.2 mm2, mean ± SEM, n = 10). Treatment for 24 h with 2% allopurinol or DMSO significantly (p 2, respectively, vs. 19.2 ± 1.1 mm2, n= 10) and this was similarly achieved by the 5% solutions (10.4 ± 0.9 and 10.2 ± 0.8 mm2, respectively, vs. 19.2 ± 1.1 mm2, n= 10). After treatment for 48 h, 30%of animals having 1 % allopurinol or DMSO remained with injury significantly (p 2, respectively, vs. 12.1 ± 0.9 mm2, n = 10); however, none treated with 2 or 5% solutions remained with any injury. Healing of this injury was confirmed microscopically and was achieved by regeneration. Thus, removing oxygen-derived free radicals stimulates the healing of ethanol-induced acute gastric mucosal injury in the rat.