The 13C-urea breath test is now a practical and readily available alternative to endoscopy- and serology-based methods for the detection of H. pylori infection. It can detect very low levels of H. pylori colonization within the stomach by assessing the entire mucosa, and avoids the risks of sampling error. We performed the 13C-urea breath test in asymptomatic volunteers and patients with gastric and duodenal ulcers in order to compare the sensitivity and specificity by measurement of H. pylori antibody by ELISA. The positive rates of H. pylori in the 13C-urea breath test was correspondent with the results from the H. pylori antibody test, although no correlation in the antibody titers and urease activities was observed between the two methods. The 13C-urea breath test was the most useful method in evaluation of eradication of H. pylori after administration of antibiotics, compared to serological and pathological methods. These results suggest that the 13C-urea breath test is highly useful for the diagnosis of H. pylori infection of the gastric mucosa.