Objective: To clarify the efficacy of combination therapy with clarithromycin and sofalcone for eradication of Helicobacter pylori. Designs: We studied 42 patients with H. pylori-positive gastroduodenal diseases, who were divided into two groups according to treatment period. Group 1 comprised 27 patients (seven with gastric ulcers, 14 with duodenal ulcers and six with gastritis) treated with a combination of clarithromycin (200 mg, three times a day) + sofalcone (100 mg, three times a day) for 3 weeks. Group 2 comprised 15 patients with chronic active gastritis treated with the same doses of clarithromycin + sofalcone but for only 2 weeks (group 2). The H. pylori status of all patients was assessed by culture, rapid urease test and histological examination at the end of treatment and 4 weeks after the end of treatment. The gastritis score, the index of intracellular periodic acid-Schiff-positive substance in the antral mucosa and the ammonia concentration in gastric secretions were also estimated before and after treatment. Results: In group 1, with over half the patients excluded from the follow-up, H. pylori was eradicated in nine out of 13 patients (69.2%) compared with six out of the complete group of 15 (40.0%) patients in group 2, without serious side effects. In these patients, significant improvements were seen in the gastritis score (P<0.025), the index of periodic acid-Schiff-positive substances in the antral mucosa (P<0.025) and the ammonia concentration in gastric secretions (P<0.02) after treatment. Conclusion: These results suggest that modification of the treatment regimen is needed, with higher doses of clarithromycin and combination therapy with proton-pump inhibition.