Fat in the proximal and distal gut inhibits intestinal transit as the jejunal brake and the ileal brake. It is unknown, however, whether the intestinal transit response to fat in the proximal vs distal gut is different. Since surgical removal of the distal small intestine induced faster transit and greater steatorrhea than removal of the proximal small intestine, we hypothesized that the ileal brake inhibited intestinal transit more potently than the jejunal brake. In six dogs equipped with duodenal (10 cm from pylorus) and midintestinal (160 cm from pylorus) fistulas, we compared intestinal transit across an isolated 150-cm test segment (between fistulas), while 0 (buffer), 15, 30, or 60 mM oleate was delivered into either the proximal (between fistulas) or the distal (beyond the midintestinal fistula) half of the gut. The half of the gut not receiving oleate was perfused with buffer. Buffer perfused into both the proximal and the distal half of the gut served as the control. A meal was administered and diverted completely out of the duodenal fistula so that the studies were all done in the fed state. Intestinal transit was measured by counting for the recovery of a radioactive marker from the temporarily diverted output of the midintestinal fistula. We found that (1) intestinal transit was inhibited more potently by oleate in the distal than in the proximal half of the gut (region effect; P < 0.01), (2) oleate inhibited intestinal transit in a load-dependent fashion (dose effect; P < 0.05), and (3) load-dependent inhibition of intestinal transit by oleate depended on the region of exposure (interaction between load and region; P < 0.01). We conclude that intestinal transit is more potently inhibited by fat-induced ileal than jejunal brake.