Résumé : A double-blind, placebo-controlled treatment study was performed in adults with antral gastritis associated with C. pylori. Patients received 20 ml of a placebo or an amoxycillin suspension (1g) two times daily for 8 days. Twenty-two patients received amoxycillin and twenty-three received a placebo. At the end of therapy 91 % (20/22) of patients treated with amoxycillin demonstrated clearance of the organism from the antrum compared to 16 % (4/23) in the placebo group (p < 0.001). Active antral gastritis resolved in 68 % (15/22) of patients in the amoxycillin group versus only 9 % (2/23) in the placebo group (p < 0.001). No significant improvement was observed in the assessment of clinical symptoms and endoscopic appearance. Reappearance of C. pylori and significant aggravation of the histological score was observed after 2 weeks in 100 % (19/19) of patients who demonstrated bacterial clearance after 8 days and had then received placebo for 14 days. Conversely, eighteen patients (not cleared from their bacteria after 8 days) received amoxycillin in single blind for 14 days. CLearance of bacteria associated with improvement or resolution of active gastritis was observed in 72 % (13/ 18) of patients. In this subgroup, 100 % (8/8) of patients observed at follow-up 1 month after stopping therapy were recolonized with C. pylori and again had histological active gastritis. These results indicate that amoxycillin suspension 2 g daily for 1 or 2 weeks is effective in treating active antral gastritis associated with C. pylori, but not in preventing relapses, which occur in all patients within one month after therapy. © 1987 Springer-Verlag.