Background & Aims Alterations in normal intestino-intestinal reflexes may be important contributors to the pathophysiology of irritable bowel syndrome (IBS). Aim: To compare the rectal tonic responses to colonic distension in female IBS patients with predominant constipation (IBS-C) and with predominant diarrhea (IBSD) to those in healthy females, fasting and postprandially. Methods Design: Using a dual barostat assembly, two-minute colonic phasic distensions were performed during fasting and postprandially. Rectal tone was recorded before, during and after the phasic distension. Colonic compliance, and colonic sensitivity in response to the distension, were also evaluated fasting and postprandially. Participants: 8 IBS-C patients, 8 IBS-D patients and 8 age and sex-matched healthy subjects (N). Results The fasting increments in rectal tone in response to colonic distension in both IBS-C (rectal balloon volume change -4.6±6.1 ml) and IBS-D (-7.9±4.9 ml) were significantly reduced when compared to N (-34±9.7 ml, p=0.01). Similar findings were observed postprandially (p=0.02). When adjusted for the colonic compliance of individual subjects, the degree of attenuation in the rectal tonic response in IBS compared to N was maintained (fasting p=0.007; postprandial p=0.03). When adjusted for colonic sensitivity there was a trend for the attenuation in the rectal tonic response in IBS compared to N to be maintained (fasting p=0.07, postprandial p=0.0 Conclusion IBS patients display a definite attenuation of the normal increase in rectal tone in response to colonic distension ('colorectal reflex'), fasting and postprandially. Alterations in colonic compliance and sensitivity in IBS are not likely to contribute to such attenuation.