Our hypothesis was that a jejunal pouch used as a rectal substitute after proctocolectomy would slow enteric transit, delay defecation, and decrease stool frequency compared to an ileal pouch so used. Twelve dogs underwent proctocolectomy; six had a jejunal pouch-distal rectal anastomosis and six had an ileal pouch-distal rectal anastomosis. After recovery, postprandial mouth-to-anus transit was slower in jejunal pouch dogs (253 +/- 18 minutes [mean +/- SEM]) than in ileal pouch dogs (112 +/- 7.9 minutes; P <0.05). Moreover, jejunal pouch dogs passed only 4.1 +/- 0.3 stools during the 12 hours after eating, whereas ileal pouch dogs passed 6.3 +/- 0. 9 stools (P <0.05). The mean frequency of proximal ileal pacesetter potentials after feeding was less in jejunal pouch dogs (12 +/- 0.4 cycles/min) than in ileal pouch dogs (16 +/- 0.3 counts/min; P = 0. 01), and jejunal pouches had more action potentials (jejunal = 82% +/- 4.3% of pacesetter potentials had action potentials, ileal = 61% +/- 3.0%; P <0.05). In contrast, gastric emptying and pouch motility, emptying, mucosal integrity, and bacteriologic and histologic properties were similar in the two groups of dogs. We concluded that the jejunal pouch operation slowed enteric transit, delayed defecation, and decreased postprandial stooling compared to the ileal pouch operation.