To evaluate the functioning and effectiveness of a 20-cm reversed jejunal segment after 75-80% massive small bowel resection (MSBR), and whether migrating polarity changes or not, we continuously measured the postoperative bowel motility (using bipolar electrodes and/or contractile strain gage force transducers) in interdigestive and postprandial conscious dogs in short- (2-5 weeks) and long-term (6-10 months) after surgery. The fasting migrating myoelectric (or motor) complex (MMC) arising from the duodenum was often interrupted at the jejunum above the proximal anastomosis and did not migrate smoothly to the reversed segment or terminal ileum. In addition, brief small discordant contractions were frequent in the jejunum above the proximal anastomosis and the proximal part of the reversed segment. The duodenal MMCs predominantly propagated to the ileum through the inherent anatomic continuity of the bowel. These findings of the MMC propagation pattern are very similar in short- and in long-term after surgery. The duration of the postprandial period without duodenal MMC activity was markedly longer in short-term, but shorter in long-term (both were significantly longer than in controls). Marked dilatation of the jejunum and reversed jejunal segment was noted across the proximal anastomosis. These results suggest that the transit time and passage of intestinal contents can be delayed and stagnated for at least 10 months after MSBR with a 20-cm reversed jejunal segment. Although, reports on the polarity of peristalsis in the reversed segment in long-term followup have been contradictory in both experimental and clinical studies, this results support the conclusion that the reversed jejunal segment maintains its inherent propagative polarity and pattern over a long postoperative period.