The study of human colonic motility under physiological conditions has proved to be an elusive goal. We have used a two-stage pernasal technique to position sensors in the human colon for the prolonged monitoring of motility in freely ambulant subjects. Nine healthy volunteers were studied for a total recording time of 263 h, each study lasting between 13 and 48 (mean 29) h. Motor activity in all regions of the large bowel was characterized by scant and irregular contractions with infrequent bursts that did not conform to any pattern. No motor coordination was apparent between different regions of the large bowel. Contractile activity throughout the large bowel was reduced to a minimum during sleep and was enhanced on waking. Meals were an inconsistent stimulus to motor activity. The technique obviates the need for colonic preparation and allows complete freedom of the subjects throughout the study. In demonstrating the practical feasibility of this mode of studying the colon, these preliminary data highlight a requirement for the availability of appropriate equipment but raise questions about the design and use of such equipment and methods of data analysis.