In order to study the effect of cholecystokinin and secretin on the endocrine function of the pancreas, we have developed an experimental model that we have applied to a total of 30 anesthetized rats stimulated with physiological or supraphysiological doses of cholecystokinin and secretin administered intravenously by continuous infusion. Our results show that the serum insulin concentration increases after the supramaximum dose of cholecystokinin is infused, while that of glucagon increases after the maximum dose of this hormone. In case of secretin, the serum glucagon level increases after the supramaximum dose, while that of insulin is not affected by any dose. We conclude that after infusion of physiological doses of cholecystokinin, the pancreatic secretion of glucagon is modified but not that of insulin, while secretin has no effect on the endocrine pancreatic secretion of either insulin or glucagon upon the same conditions.