Reconstructing the enteric tract after near-total proctocolectomy by interposing a jejunal pouch between the distal ileum and the distal rectum slows small intestinal transit and decreases the number of stools per day compared to a conventional ileal pouch-distal rectal reconstruction. Our hypothesis was that the jejunal pouch operation brings about these results by protecting the ability of the ileal mucosa to secrete peptide YY, thus augmenting the hormonal ileal brake on small intestinal transit and decreasing the stool frequency. In five jejunal pouch dogs and five ileal pouch dogs, more than 6 months after the operation, serum peptide YY concentrations were determined before and at 30-minute intervals for 180 minutes after a standard meal. Fasting serum concentrations of peptide YY, measured by radioimmunoassay, were greater in jejunal pouch dogs (mean ± SEM, 1340 ±143 pg/ml) than in ileal pouch dogs (804 ±52 pg/ml; P <0.01). Postprandial peptide YY concentrations in jejunal pouch dogs were also greater at 30 minutes (jejunal pouch = 1524 ±131 pg/ml, ileal pouch = 913 ±67 pg/ml; P = 0.01) and 60 minutes after the meal (jejunal pouch = 1723 ±250 pg/ml, ileal pouch = 1001 ±70 pg/ml; P = 0.05) and peaked sooner (jejunal pouch = 81 ±17 minutes, ileal pouch = 147 ±12 minutes; P = 0.01). We concluded that the jejunal pouch operation results in greater ileal fasting and postprandial secretion of peptide YY than the ileal pouch operation. The greater release may account, in part, for the slower small bowel transit and decreased number of stools after the jejunal pouch operation.