The relative blood flow distribution within the small intestine of anesthetized cats was investigated during resting conditions and when superior mesenteric blood flow was increased 15--85% by the intravenous infusion of secretin, cholecystokinin (CCK), or isoproterenol. Radioactive microspheres of 15 mum diameter were injected into the superior mesenteric artery and shortly thereafter intestinal segments were removed and dissected into mucosal, submucosal, and muscularis fractions. Tissue weights and the radioactivity of each were determined. During secretin-induced mesenteric vasodilatation there was a significant redistribution of blood away from the jejunal mucosa to the submucosa. During CCK and isoproterenol infusions there were significant increases in mucosal and decreases in submucosal blood flow. No significant changes were observed in muscularis flow. There was no apparent relationship between the percent increase in SMBF and the relative blood flow distribution changes observed. The results indicate that while secretin, CCK, and isoproterenol increase superior mesenteric blood flow, they also affect blood flow distribution within the mucosa and submucosa.