Sixty-seven conscious rats prepared with chronic gastric fistula were studied to examine the effect of vagotomy on gastric secretory responses to medial amygdaloid stimulation. Gastric acid output was significantly increased by electrical stimulation of the medial amygdaloid nucleus, and the increases in acid secretion were completely eliminated by vagotomy. However, in rats subjected to stimulation of the medial amygdaloid nucleus plus vagotomy, acid output was almost same as that in only vagotomized rats. And vagotomy itself decreased the acid secretion significantly. These results indicate that the influence of electrical stimulaton of the medial amygdaloid nucleus on acid secretion is carried largely via vagus nerves. And also, without electrical stimulation of medial amygdaloid nucleus, acid secretion is controlled by way of vagus in rats. Plasma gastrin concentrations were measured following stimulation of the medial amygdaloid nucleus. Plasma levels of gastrin were not significantly altered by stimulation of the medial amygdaloid nucleus with or without vagotomy. It is therefore inferred from the above results that the facilitatory influence of the medial amygdaloid nucleus on the gastric acid secretion is mediated chiefly via vagal activity and that gastrin is not responsible for the increase in acid secretion in this process.