This study was undertaken to investigate the effect of medial amygdala on the gastric acid secretion and plasma gastrin concentration in the rats with chronic gastric fistula. After the medial nucleus of amygdala was damaged bilaterally by radiofrequency a. c. through stereotaxically inserted electrodes, the gastric juice was collected in the basal and histamine-stimulated states for 1 hour. The gastric juice was also collected while the medial nucleus of amygdala was stimulated with biphasic square wave in the both states. After the collection of the gastric juice, blood samples were drawn from the abdominal aorta for the radioimmunoassay of plasma gastrin. The results were as follows: 1) The damage of the medial amygdala significantly decreased the gastric juice volume and the acid output in the histamine-stimulated state. 2) The electrical stimulation of the medial amygdala significantly increased the gastric juice volume and the acid output in the histamine-stimulated state, and the acid output in the basal state. 3) The damage of the medial amygdala significantly decreased the plasma gastrin concentration but the electrical stimulation of the medial amygdala did not affect the plasma gastrin concentration. It is therefore suggested that the medial amygdala has a facilitatory influence on the histamine-stimulated gastric acid secretion in rats, and the influence may not be attributed to gastrin release.