Prolonged absence of food from the gut is said to cause hypoplasia of the intestine and pancreas. Whether gut and pancreatic hormone secretion is correspondingly altered is not known. As total parenteral nutrition (TPN) and nil per os is now used to treat many gastrointestinal disorders, we investigated what effect intralumenal starvation of the gut, yet adequate nutritional support had on gastrointestinal and pancreatic hormonal release in humans. Gut hormone release was studied before and after a standard meal in 9 patients with Crohn's disease treated by nil per os and TPN for a mean of 25 days (range 18–52). Subsequently after a variable period of normal oral diet (mean 156 days; range 38–395), the same meal study was repeated. Fasting and peak postprandial concentrations of gastrin, motilin, GIP, secretin, pancreatic polypeptide, pancreatic glucagon, and VIP immediately after a period of nil per os and TPN (NPO-TPN) were not significantly different from the second meal study after refeeding (RF) and were equivalent to levels observed in healthy subjects. Although the postprandial rise in glucose was identical with both meals, after NPO-TPN the peak insulin response was significantly (p < 0.001) lower than the normal levels after refeeding. With both meals, basal enteroglucagon was similar, yet a significantly (p < 0.01) higher peak level occurred after NPO-TPN. To assess the effect of TPN (mean 22 days, range 18–25) on gut hormone release, we also undertook sequential hormone measurements before, during, and after TPN in 8 other patients. No significant change in plasma gastrin, motilin, pancreatic polypeptide, GIP, secretin, or enteroglucagon was observed as a consequence of TPN. Thus after TPN and nil per os in humans the fasting and postprandial gut endocrine response is well maintained. Higher postprandial levels of enteroglucagon may reflect greater ileal exposure to the nutrient load as a consequence of decreased transit time, while the diminished insulin response, yet identical, glucose levels may point to peripheral insulin hypersensitivity after TPN.