Electrical events and flow in the canine small intestine in vivo were studied. The transit of a small radioactive bolus injected into the jejunum was monitored by counting from a Biebl loop. After feeding, the rate of propulsion of the bolus varied within a narrow range. When food and water were withheld for more than 12 h, transit of the bolus became highly variable. The variability increased at about the same time as the onset of the migratory myoelectric complex associated with fasting. Electrical recordings from the intestinal muscle demonstrated that the bolus was propelled into the loop in advance of the band of intense spike potentials which travels along the small intestine in the fasted state. The bolus was cleared from the loop when the spike potentials reached this segment. Variability of transit after prolonged fasting can be explained by the variability in the rate of migration of the phase of intense spike potentials and the timing of the injection of the bolus in relation to the component phases of the electrical complex. Flow is highly dependent upon the electrical activity and the resulting contraction patterns of the small intestine, which are themselves dependent upon feeding.