Orocecal transit time is studied in individuals with irritable bowel syndrome (IBS) of both the constipation-dominant, diarrhea-dominant, and mixed form using the lactulose hydrogen breath test for orocecal transit time through the gut. Data are compared to those of healthy volunteers. The peak value of fermentation as read by hydrogen levels is captured after passage of the orocecal segment in the colon. Comparison are made between IBS patients and healthy subjects as regards orocecal transit time and peak fermentation in the cecum.