The role of the canine ileocolonic sphincter (ICS) in influencing transit of fluids and absorption of water in the ileum was assessed in loops with or without the ICS. Two sets of four dogs each were equipped with isolated ileal loops 40 cm long, attached to the intact bowel through a neuromuscular bridge. In one set, the loop included the ICS and it terminated in an end colostomy; in the other, the loop ended immediately proximal to the ICS, as an ileostomy. Electrical and mechanical signals were recorded from serosal electrodes and strain gauges, respectively, during perfusion of loops with an isotonic solution at rates from 0.7 to 10.0 ml/min. Loops without an ICS propelled fluid by steady, continuous flow at all rates of perfusion; loops with the ICS in place moved fluids in this way only at 10 ml/min. At greater rates of perfusion, fasting cycles of motility were inhibited in all loops and a random pattern of motility developed; this presumably facilitated more steady flow of fluids. At the slowest rate of perfusion, transit times were longer when the ICS was present, but at faster rates both loops showed similar transit times. Presence of the ICS was associated with increased volumes of fluid in the loop and increased absorption of water, especially when loops were perfused slowly. The canine ICS influences flow of saline and absorption in the terminal ileum, but only when flow rates are low.