Abstract Synthetic bombesin was infused at a dose of 20 pmoles/kg/min for 10 min into the cranial pancreaticoduodenal artery of anesthetized dogs. Plasma immunoreactive glucagon concentrations in the cranial pancreaticoduodenal vein as well as in the femoral artery were concurrently and slowly elevated. However, the net release of glucagon from the pancreas did not increase significantly during infusion of bombesin. Plasma immunoreactive insulin concentrations in the pancreatic vein were transiently raised, and a delayed rise was noted in arterial plasma IRI. Net release of insulin was significantly augmented during infusion of the tetradecapeptide. Plasma glucose levels did not change after bombesin. These results indicate that the gastrointestinal tetradecapeptide may stimulate secretion of both insulin and gut glucagonlike immunoreactivity in the dog.