Canine gastrointestinal motility is studied at present in animals confined to a small cage or sling. The aims of this study were to record colonic activity over a 24-h period in eight dogs by an ambulatory method. Motility signals from implanted strain gauges were processed and stored via a portable battery-operated amplifier and digital recorder housed in a jacket. Ambulant interdigestive activity was the same as observed in laboratory experiments, with migrating colonic motor complexes (CMCs) and infrequent giant contractions (GCs). Feeding caused a multiphasic alteration in motility for 582.1 +/- 18.1 min (mean +/- SE). There were four distinct phases. During the "early" (0-2 h) postprandial period, phase 1 (mean duration: 55.1 +/- 4.0 min), which was distinguished by CMCs of high frequency and elevated amplitude in the proximal colon, and phase 2 (78.2 +/- 6.2 min), which had CMC characteristics similar to those in the interdigestive period, occurred. Phase 3 (218.8 +/- 13.6 min), a further period of increased motility, and phase 4 (339.1 +/- 14.0 min), characterized by low-amplitude long-duration CMCs, occurred during the "late" (2 h onward) postprandial response. With the exception of phase 3, postprandial phases were not always present following food intake, and their expression was markedly influenced by variations in meal time and by defecation immediately following feeding. Spontaneous defecation was characterized by a variety of motor profiles, with a GC accompanying two-thirds of episodes. We conclude that a more complete picture of canine colonic motility has been documented because of the development of the ambulatory system.