The control mechanism of canine colonic motor activity measured by means of chronically implanted force transducers was studied by comparing diurnal changes and migrating patterns in control dogs and dogs with innervated and extrinsically denervated colonic loops. Five force transducers (C1-C5) were placed on the colon, and the middle colon was transected to construct a loop including C2 and C3 transducers. Colonic continuity was established by an end-to-end anastomosis. In the fasted state, colonic motor complexes of 8-13 minutes' duration were observed to occur at intervals of 22-32 minutes in all three groups, but response to feeding was clearly different; significant enhancement of the colonic motor indexes lasting for 8-16 hours after feeding, which was observed at all recording sites in control dogs, was identified only in the proximal and distal colon in dogs with innervated and extrinsically denervated loops. In the innervated loop, significant enhancement of the motor indexes was observed only in the first 2 hours after feeding. In the extrinsically denervated loop, feeding did not induce any response. In both groups with loops, greater than 40% of the motor complexes that occurred in the proximal colon migrated to the distal colon directly across the anastomosis and less than 20% propagated to the loop. In addition, the migration time between the proximal and the distal colon was greatly reduced in both groups with loops compared with that in the control group. Another change observed within the loop was an increase in numbers of retrograde migrating colonic motor complexes. It is concluded that colonic motor activity is under the predominant control of intraluminal contents in the digestive state but that extrinsic nerves may play an important role in the response observed in the innervated loop in the first 2 hours after feeding, which should be defined as the gastrocolonic response in dogs. In the interdigestive state, the intrinsic nervous system and/or humoral factors may control the occurrence of colonic motor complexes.