The mechanisms of acute gastric mucosal injury caused by non-steroidal antiinflammatory drugs (NSAID) are not fully understood. Recent work suggests that free oxygen radicals are probably contributary. The present work was designed to study the ability of some free radical scavengers, viz, allopurinol, vitamin C and vitamin E, to protect against the mucosal injury produced by oral administration of indomethacin. The effect of these agents on gastric acid secretion as well as its output per hour was measured using the titrable technique. The concentration of pepsin and mucus content in the gastric juice were also determined, and for the assessment of gastric ulceration, the preventive index was calculated. Moreover, to study the effect of the three antioxidants" Allopurinol, Vit. C & Vit. E" on gastric mucosal prostaglandin £2 synthesis, independent groups of rats were employed. It was found that Allopurinol, vit. C, Vit E did not change indomethacin - induced drop in gastric mucosal prostaglandin £2. Thus, it could be concluded that free radicals play a role in the pathogenesis of peptic ulcer and that free radical scavenger can, in part, protect against indomethacin - induced gastric injury.