Vascular effects of raising local arterial concentration of pentagastrin (2-1,500ng/ml), secretin (0.2-150mU/ml), and cholecystokinin (0.2-150mU/ml) in the duodenum, jejunum, heart, kidney, forelimb, spleen, and the skin and muscle of the forelimb were studied in 54 anesthetized dogs. Secretin produced similar vasodilation in all organs. The minimal increment in local blood secretin concentration for vasodilation ("concentration requirement") was between 7 and 32 mU/ml. Pentagastrin produced vasodilation only in the duodenum and jejunum and the concentration requirement was between 25 and 50 ng/ml. Cholecystokinin did not affect vascular resistance of the forelimb, skin, or muscle. In the heart, kidney, and spleen, cholecystokinin produced vasodilation but the concentration requirement was above 21-33 mU/ml. In contrast, vasodilation in the duodenum and jejunum appeared when cholecystokinin concentration was increased by only 2.5 mU/ml. Furthermore, almost all its vasodilating effect occurred below an increment of 10 mU/ml. Comparison of our data with the reported cardiovascular adjustments and blood concentration of gastrointestinal hormones following a meal suggests that cholecystokinin may contribute to postprandial intestinal hyperemia.