Antacids are more effective than placebo, and their efficacy is comparable to that of H2-blockers in gastric ulcer healing even though the healing time is about 2 weeks longer than with H2-blockers. Some observations in animals and healthy subjects may indicate that antacids (particularly those containing aluminium hydroxide) have a protective effect on the gastroduodenal mucosa in that they increase the production of prostanoids and sulphydryl-containing compounds. We showed that 10 days' treatment with high-dose antacids (Maalox TC) is able to increase 6-keto-PGF1 alpha production from cultured biopsy specimens of patients with gastric ulcer. These data could constitute a further indication in the treatment of peptic disease.