BACKGROUND/AIMS: In the previous reported studies, only two thirds of irritable bowel syndrome (IBS) patients were found to have rectal hypersensitivity. Furthermore visceral hypersensitivity is the most frequent finding in constipation-predominant IBS patients. The aims of this study were to determine the levels of the sigmoid discomfort thresholds in patients with IBS, and we wanted to determine the relationship between the sigmoid discomfort thresholds and the symptoms of IBS. METHODS: 18 Rome II positive IBS patients and 9 normal controls were recruited. A sigmoid bag catheter was endoscopically placed, and bag inflation was performed by using a barostat. The sigmoid discomfort thresholds were measured by using an ascending series and a tracking procedure. RESULTS: The sigmoid discomfort thresholds, as measured by using an ascending series, for the patients with IBS (27.8+/-7.3 mmHg) was significantly lower than that for the controls (36.7+/-10.0 mmHg) (p<0.05). There was no significant differences in the sigmoid discomfort thresholds using the tracking procedure between the IBS patients (31.7+/-9.9 mmHg) and the controls (37.8+/-9.7 mmHg) (p>0.05). There were no significant differences in the sigmoid discomfort thresholds using the ascending series and the tracking procedure between the constipation predominant IBS patients and the diarrhea predominant IBS patients. CONCLUSIONS: The sigmoid discomfort threshold, as measured by using an ascending series, for the patients with IBS was significantly lower than that of the controls. However, there was no correlation between the sigmoid discomfort thresholds and the IBS symptoms.