In order to elucidate the mechanism of stress ulceration, which is mainly involved with the corpus mucosa of the stomach, the aerobic energy metabolism of the corpus mucosa of rats, rabbits and humans was investigated and compared with those of the antral mucosa as well as other organs such as heart, kidney and liver. The results showed that the activities of respiration and oxidative phosphorylation and the concentration of the respiratory chain components were far greater in the corpus mucosa than in the antral mucosa, the activities in the former being almost equal to that of the highly aerobic tissue, kidney cortex. Furthermore, the endogenous respiratory rate (in the absence of added substrate) was also much higher in the corpus mucosa than in the antral mucosa, indicating that oxygen demand at resting state (during the period of H+ secretion) is also higher in the corpus mucosa. We conclude that in the corpus mucosa of the stomach the aerobic energy metabolism is predominant. It is suggested that circulatory insufficiency may easily result in cell damage mainly of the corpus mucosa due to energy deficit.