An electromyographic technique was used to study the changes in postprandial motility induced by jejunal and ileal resection and jejunal bypass (50% reduction of total length of small bowel). Electrodes were implanted in rats throughout the intestine. Compared to control animals, the duration of postprandial interruption of the myoelectric complex (DIMC) was rapidly increased after jejunal resection, more gradually augmented after jejunal bypass, and remained constant after ileal resection. The frequency of occurrence of spike bursts during the postprandial period was significantly decreased in the short remaining proximal segment after jejunal resection and was not changed in the ileum. The jejunal bypass induced no change in the frequency throughout the remaining bowel. Ileal resection was followed by a decrease on the jejunum. The percentage of slow waves superimposed by a spike burst remained constant after jejunal resection and bypass but was significantly decreased after ileal resection on the whole remaining intestine. These results show important modifications in postprandial motor activity of the small bowel, which appear rapidly after jejunal resection, more gradually after jejunal bypass, and which are less pronounced after ileal resection. This electromyographic study emphasizes the role of intestinal motility in the development of adaptation after small bowel resection or bypass.