BACKGROUND/AIMS: The purpose of this study was to discover the physiologic difference of a postprandial motor response in different segments of the colon between patients with irritable bowel syndrome and healthy subjects. METHODS: Irritable bowel syndrome patients are categorized into three groups according to their main symptoms; loose stool-dominant (A, n=5), abdominal pain-dominant (B, n=5), constipation-dominant (C, n=6) and the normal control group (n=5). The intraluminal pressure activity was measured with a colonoscopically positioned multilumen manometric catheter. The change of the colonic motility index (MI) is presented as a percent change (mean+/-SE%) over the basal period in response to a meal. RESULTS: 1) In the transverse, descending and sigmoid colon of healthy subjects, the percentage changes in the basal MI during the first 30 min after the meal are significantly increased (p < 0.05-0.01). 2) In the sigmoid colon, the percentage changes in the basal MI during the first 30 min after the meal were 62+/-18 in A, 29+/-18 in B, 12+/-8 in C and 306+/-102% in heathy subjects respectively, which shows a significant difference between the MI of control and healthy subjects (p < 0.05). 3) In B and C, the percentage changes in the basal MI during the first 30 min after the meal in the descending colon were 105+/-38, 11+/-7, respectively, which shows a significant difference between the two groups (p < 0.05). In A and C, the percentage changes in the basal MI during the first 30 min after the meal in the sigmoid colon was 62+/-18, 12+/-8, respectively, which shows a significant change between the two groups (p < 0.05). CONCLUSION: This study suggests that postprandial intraluminal pressure differences play a role in the pathophysiology of irritable bowel syndrome.