Complexes of high amplitude action potentials have been shownn to occur in the stomach and duodenum of fasting dogs. These complexes recur at regular intervals as long as the animal is fasting, and they are propagated aborally over the whole lenght of the small bowel. The cyclical pattern is replaced by the digestive of "fed" pattern of activity upon feeding. Therefore the pattern has been known as the interdigestive myoelectrical complex. Studies in herbivorous species however, in which the flow of digesta is more or less continous have show that cyclically recurring migrating complexes can be demonstrated in these species as well. Thus, the term "migratory myoelectrical complex" may be more appropriate. Propagation of the complex is not dependent upon continuity of the bowel wall nor movement of luminal contents. Replacement of the complex by the digestive pattern of activity upon feeding and the restitution of the interdigestive pattern at the end of the digestive phase seem to be under nervous as well as hormonal control. The interdigestive complex in the dog has been looked upon as a "housekeeper" which sweeps the bowel clear of contents at the end of the digestive phase. Aspects of possible physiological significance of the complex are: periodic elimination of refluxed duodenal contents from the stomach and prevention of bacterial colonization of the small bowel by the colonic flora. The existence of propagated complexes has not been demonstrated in man, but there is increasing evidence for cyclical activity which fits the pattern.