A relationship between duodenal myoelectric or motor activity and exocrine pancreatic secretion as well as plasma gut hormone levels has been investigated in fasted dogs, fed dogs, and dogs that were stimulated with exogenous gut hormones. Pancreatic secretion showed typical periodicity in phase with the myoelectric or motor activity of the duodenum. Fasting pancreatic bicarbonate and protein secretion reached peaks during phase III of the interdigestive migrating motor complex (MMC) cycle that were significantly larger than nadir levels occurring during phase I of the cycle. These fasting bicarbonate and protein peaks reached, respectively, approximately 9 and 30% of the highest postprandial outputs and 4 and 14% of the maximal secretory capacity elicited by secretin or CCK. They were accompanied by a significant rise in plasma motilin, gastrin, and pancreatic polypeptide (PP), but only exogenous motilin given in physiological dose induced motility pattern and pancreatic secretion similar to those observed during phase III. Feeding interrupted both motor and secretory MMC cycle, increased the pancreatic secretion to approximately 40-60% of the maximal secretory capacity, and was accompanied by increments in plasma gastrin, cholecystokinin (CCK), secretin, and PP. None of these hormones applied alone in physiological dose was capable of reproducing the postprandial inhibition of MMC cycles. We conclude that the pancreatic secretion in fasted dogs fluctuates periodically in phase with duodenal motility, but the phase III peak secretory outputs represent only minute fractions of the maximal secretory capacity and can therefore be ignored in regular testing of pancreatic secretion.