BACKGROUND/AIMS: This study was designed to evaluate whether the result of 13C-urea breath test (UBT) was influenced by fasting status and to assess the adequate test duration for sample collection. METHODS: Twenty-five volunteers were enrolled in this study. Their results were concordant in histology and standard (fasting) UBT for the diagnosis of Helicobacter pylori (H. pylori) infection. Standard UBT was performed after 4-hour-fasting and nonfasting UBT was performed within 1 hour after each meal for the same subjects at one week interval. The breath samples were collected just before and at 5, 10, 15, 20, 25, 30, 35, 40, 50, and 60 minutes after test meal (HelikitTM) and analyzed by isotope ratio mass spectrometer. H. pylori infection was defined as delta13CO2 at 30 minutes was over 4%. RESULTS: Of 25 volunteers, 13 were infected by H. pylori. Diagnosis of H. pylori the case in which infection was completely concordant in both standard and nonfasting states. In H. pylori infected group, delta13CO2 was significantly decreased in nonfasting state than standard state, and the mean delta13CO2 of both states was the highest at 20 minutes after test meal. Ten minutes were sufficient to obtain deltaCO2 for diagnosis of H. pylori infection. CONCLUSIONS: The diagnosis of H. pylori infection is not affected by whether UBT using 75 mg of 13C-urea containing HelikitTM is performed in nonfasting state or its test duration is shortened.