It has been recently reported that cingulate cortex mar facilitate gastric acid secretion, but its facilitatory mechanism on the gastric acid secretion is still unclear. This study was undertaken to investigate the facilitatory mechanism of the cingulate cortex upon gastric acid secretion in rats. Twenty¡¤three male albino rats were divided into the cingulate(N= 13) and the operated control(N= 10) groups. The cingulate group in which cingulate cortex was removed by suction through a slit-shaped opening on each side of, and parallel to, the sagittal suture. In the operated control group, the surgical procedure was ended with the skull opening and the incision of dura mater. The gastric juice was collected via a chronic gastric cannula after 24 hours of fast, with water ad libitum. The juice was collected continuously for 6 hours, starting 3 hours prior to the injection of gastric secretagogue, pentagastrin(12 μg/kg) or histamine dihydrochloride (320 μg/kg). Three one¡¤hour samples were obtained before ana after the administration of each secretagogue. The two agents were injected separately and subcutaneously at intervals of 1 week, the blood samples were drawn from the abdominal aorta for the radioimmunoassay of postprandial plasma gastrin concentration in response to the forced feeding of 10% cod liver oil. 1) After pentagastrin administration, the volume of gastric juice tended to decrease, but its acidity tended to increase in the cingulate group compared with those of the operated control group. However, there was no any difference in the acid output between the two groups. 2) Histamine-stimulated acid output and volume of the gastric juice of the cingulate group decreased significantly compared with those of the operated control group, while there was not significantly different in the acidity between the two groups. 3) Before pentagastrin or histamine administration, any change was not observed in the gastric acid secretion following the cingulate cortical ablation. 4) Postprandial plasma gastrin concentration in response to the forced feeding of 10% cod liver oil was insignificantly lower in the cingulate group than in the operated control group. It is inferred from the above results that the cingulate cortex exerts a facilitatory influence upon the histamine-stimulated gastric acid secretion in rats, and its influence may not be mediated by the stimulation of gastrin secretion.