This study was conducted to investigate whether an electrical stimulation of medial amygdaloid nucleus in rats increases pancreatic secretion. And an involvement of vagus nerve or plasma secretin in this process was also studied. In fasting rats anesthetized with urethane, a monopolar stainless steel electrode was stereotaxically inserted into the right medial amygdaloid nucleus. Pancreatic juice was collected for 20 minutes, during which physiological saline or 0.01 N HCI (0.18 ml/min) was perfused into the duodenum with or without bilateral subdiaphragmatic vagotomy. In the medial amygdaloid group, an electrical stimulation was continuously applied to the medial amygdaloid nucleus during the perfusion period. After collection of pancreatic juice, blood was drawn from the abdominal aorta for determination of the plasma secretin level. The results were as follows: 1) The electrical stimulaion of the medial amygdaloid nucleus did not influence the pancreatic secretion in response to intraduodenal saline perfusion. 2) The stimulation of the medial amygdaloid nucleus significantly increased the pancreatic secretory response (volume, bicarbonate output) to the intraduodenal 0.01 N HCI perfusion, and the increases were abolished by vagotomy. 3) The plasma secretin concentration after the intraduodenal 0.01 N HCI perfusion was higher than that after the saline perfusion. However, neither the electrical stimulation of the medial amygdaloid nucleus nor vagotomy affected the plasma secretin concentration during the intraduodenal perfusion with saline or 0.01 N HCI. It is, therefore, suggested that the medial amygdaloid nucleus facilitates the pancreatic secretion (volume, bicarbonate) elicited by intraduodenal HCI perfusion through the vagus nerve.