The disruptive effect of food and food components on the migrating myoelectric complex (MMC) was studied in conscious dogs. Three types of test meals were fed, and the interval between feeding and the reappearance of the first phase III of the MMC was determined. When commercial dog food was used a linear relation was observed btween the quantity of food (expressed as kcal/kg body wt) and the duration of the disruption of the MMC. Equicaloric amounts of the three major food components disrupted the MMC pattern for periods of time that were related to the nature of the food: the effect of arachis oil lasted longer than that of sucrose and much longer than that of milk protein. Medium chain triglycerides had a potent disruptive effect. Mixtures of these food components produced a disruptive effect that could not be calculated from the individual effect of each component. Phase III of the first and second MMC after feeding started at a lower level of the intestine than after a long fast. The duration of disruption of the MMC after a meal depends much more on the physicochemical composition of the food than on its volume or amount of calories.