The effects of the freeze-dried aqueous extract from red mangrove bark on gastric ulceration induced by ethanol-hydrochloric acid were studied in rats. Mucosal damage was compared with that given with cimetidine. The effects of these agents on the quantity and quality of the gastric mucus were also determined. Oral treatment with red mangrove extract at 500 mg/kg body weight (b.w.) gave the highest level of gastric protection. Mucus content was increased and it was accompanied by a proportional increase in proteins. The group, which received cimetidine, showed no effect on the mucus secretion induced in this experimental model.