The small intestine in vivo is capable of a variety of patterns of contraction. Many of these patterns can result in the propulsion of intestinal contents. In the healthy human, dog, and rat propulsion is caused by at least two different patterns. One pattern seen in the fasted animal results in the intermittent movement of material out of any given segment of bowel and then the steady movement of this material down the bowel. In the fed state, there is a more or less uniform net aboral movement of contents. Although there are two distinct patterns, the net effect, in the rat at least, is that over long periods of time propulsion is of equal velocity in the two conditions. In certain disease states, other patterns of motility can be responsible for propulsion. These patterns can propel material orally as well as aborally. In light of these contractile patterns, it would not be surprising to find that propulsion in isolated segments can be affected by several different patterns of activity. Also, it would not be surprising to find that the various subsystems controlling motility can be integrated in several different modes to produce such patterns.