AbstractDiurnal changes in canine colonic motility were investigated by means of chronically implanted force transducers. A characteristic of the colonic motor profile in the fasted state was the occurrence of colonic motor complexes consisting of tonic contractions superimposed with phasic ones. On feeding, motor complexes were immediately induced in the whole colon and continued to occur at significantly shorter intervals than those in the fasted state, but the duration and the amplitude of the colonic motor complexes were not affected by feeding. This increased activity period lasted for 8–16 h after feeding, and 83.3% of the defecations were observed in this period. Of the defecations 33% occurred in the first 2 h after feeding (P<0.05). More than 80% of the giant migrating contractions associated with defecation propagated from the middle to the distal colon, and the start of faeces evacuation coincided with the end of the relaxation period of the distal colon preceding the arrival of the giant migrating contractions. More than 90% of the giant migrating contractions not associated with defecation migrated from the proximal to the middle colon. More than 60% of the colonic motor complexes migrated in an aboral direction and about 18% of them in an oral direction. These results suggest that (1) defecations tend to occur immediately after feeding; (2) the regional distribution of giant migrating contractions was different between those associated and not associated with defecatio