Massive small bowel resection that results in short bowel syndrome brings about regulatory mechanisms in the remaining intestine aimed at preventing the ensuing malabsorption. The purpose of the present study was to determine the role of pancreatic and biliary secretions in intestinal adaptation after small bowel resection. To do so, both pancreatic and biliary fluids were prevented from reaching the lumen of most of the small bowel. Four groups of animals were prepared: I) control group; II) eighty percent small bowel resection; III) duodenoileal by-pass; and IV) duodenoileal by-pass plus small bowel resection. After a fifteen days recovery period, the following were recorded: animal weight; plasma protein, BUN, cholesterol, glucose, and Ca++; the length and diameter of the jejunum and ileum, the height of the mucosal layer, and microvilli density. Intestinal adaptation was excellent in animals after small bowel resection. All animals in group IV died due to severe malabsorption. Diversion of pancreatic and biliary juice in animals with duodenoileal by-pass did not prevent intestinal adaptation. We conclude that the effect of pancreatic and biliary juice on intestinal adaptation is additive to that of other putative hormonal mechanisms.