In November 2000, eradication therapy for Helicobacter pylori infection was approved under the present Japanese system of health insurance. Before the approval, the Japanese guideline of "Diagnosis and Treatment of H. pylori infection" was made by the guideline committee of the Japanese Society for Helicobacter Research. Indications for H. pylori eradication therapy were classified into three groups: (A) recommended: gastric and duodenal ulcers; (B) recommended and managed at a specialized institution: low-grade gastric mucosa-associated lymphoid tissue lymphoma; (C) current studies of the significance of the therapy: following endoscopic mucosal resection of early gastric cancer and gastric surgery for gastric cancers, hyperplastic gastric polyp, atrophic gastritis, and nonulcer dyspepsia. The first-line therapy regimen recommended is 1 week of triple therapy with a proton pump inhibitor standard dose twice a day, amoxicillin 750 mg bid, and clarithromycin 200 or 400 mg bid. The reasons for preferring this regimen are to avoid extensive use of metronidazole, which is allowed for treatment of Trichomonas infection in Japan, and the low rate of emergence of clarithromycin-resistant H. pylori with amoxicillin co-therapy. For second-line therapy patients should be referred to specialists, who can examine the susceptibility of H. pylori isolates against antibiotics and have much experience with this therapy.