Using an intraluminal probe supporting eight groups of electrodes, the myoelectrical activity of the proximal, transverse, and distal colon was recorded during 24-h sessions in 10 healthy subjects receiving evening and noon meals (greater than 800 kcal) and breakfast (less than 300 kcal). At each colonic site considered, the electromyograms exhibited two kinds of spike bursts: (a) short spike bursts localized at one electrode site and appearing rhythmically at a frequency of 10.6 +/- 0.3/min and (b) long spike bursts isolated or propagated orally or aborally. A peculiar pattern consisting of nearly permanent short spike bursts at a rate of 6.7 +/- 0.4/min was observed at the rectosigmoid junction. Computerized analysis of the duration of each kind of spike burst showed that the long spike burst activity increased by 63%-129% (p less than 0.05) during 2 h after each meal (but not after breakfast) at each colonic site. Furthermore, a significant (p less than 0.05) decrease in the long spike burst but not short spike burst activity was observed during sleep. These results provide evidence for circadian variations of colonic motility associated with eating and sleeping in the healthy human.