OBJECTIVES: I. Evaluate the response of gastric lymphoma of mucosa-associated lymphoid tissue (MALT) to treatment for Helicobacter pylori infection with antibiotics (amoxicillin, clarithromycin, tetracycline, and metronidazole) and with gastric acid inhibitors (omeprazole and bismuth subsalicylate). II. Correlate response with endoscopic tumor grade and clinical and pathological parameters. III. Assess the incidence of H. pylori infection in patients with gastric MALT lymphoma.