PURPOSE:The normal response to rectal distention is a relaxation of the proximal anal canal (PAC). We hypothesized that this mechanism would require a gradient of pressure and time to preserve continence.METHODS:Sixteen volunteers (10 male), mean age, 41.5 (range, 24‐60) years, were studied using an eight port axial catheter with a compliant balloon at its tip. Relaxation was induced by a small volume of rectal distention (15‐30 ml of air) and was recorded until recovery of resting anal pressure (RAP). Duration of relaxation was measured until recovery of RAP. Amplitude of relaxation was determined between RAP before rectal distention (RAP‐BR) and pressure at the point of maximum relaxation (RAP‐PMR). Gradient of pressure was determined by comparing RAP‐PMR in the high‐pressure zone (HPZ) and PAC. Contraction in the distal anal canal was interpreted as external anal sphincter contraction (EASC) and was compared with RAP‐PMR in the HPZ.RESULTS:Relaxation was significantly greater in PAC than in HPZ (50vs.36 percent;P=0.001). RAP‐PMR was significantly higher in HPZ than in PAC (30.7vs.12.6 mmHg;P= 0.001). EASC was observed in six patients and did not show significant difference with RAP‐PMR in HPZ (39.7vs.36.3 mmHg; not significant). Relaxation began at the same time in all levels but lasted significantly longer in PAC compared with HPZ (13.5vs.9.4 sec;P=0.003).CONCLUSION:Anal relaxation induced by small volume rectal distention involves a gradient in the pressure and time of relaxation between PAC and the HPZ.