Effects of medial amygdaloid stimulation on pancreatic exocrine secretion were investigated in anesthetized rats with pyloric ligation. During intraduodenal 0.01 N HC1 perfusion, the electrical stimulation of the medial amygdaloid nucleus augmented significantly the HCI-induced pancreatic secretion of water and bicarbonate output. The duodenal acidification significantly increased secretin concentration in plasma. The effects of medial amygdaloid stimulation were also tested in the rats that received a small dose of porcine secretin. Although the amount of secretin infused was not enough to increase the pancreatic exocrine secretion, the stimulation of the medial amygdaloid nucleus significantly increased flow and bicarbonate output. The augmented pancreatic secretory responses to electrical stimulation of the medial amygdaloid nucleus were abolished by bilateral truncal vagotomy. However, the medial amygdaloid stimulation was not effective in stimulating pancreatic secretion in the rats perfused with isotonic saline. From these results, it is suggested that the medial amygdaloid nucleus plays a stimulatory role in pancreatic exocrine secretion via vagus nerves and that a certain level of plasma secretin is needed for the medial amygdaloid stimulation to be effective.