Peptide YY (PYY) which is most likely to mediate colonic inhibition on digestive organs is also a potent vasoconstrictor. However, very little is known about the effect of circulating PYY on splanchnic blood flow. This study examined the effect of systemic administration of peptide YY on splanchnic circulation and exocrine pancreas in dogs. Under secretin stimulation, intravenous administration of PYY (0.1, 0.5, 1 and 2 micrograms/kg) significantly decreased pancreatic secretion volume and blood flows in the pancreatic tissue, the superior mesenteric artery and the celiac artery in a dose-related manner. At the same time, PYY increased mean blood pressure. Under secretin plus cholecystokinin stimulation, PYY (1 micrograms/kg) significantly inhibited pancreatic secretion volume and protein output. This study first shows that PYY potently reduces celiac arterial blood flow as well as intestinal blood flow at such doses that PYY inhibits exocrine pancreatic secretion.