Effects of 3,4,5-trimethoxy-N-(3-piperidyl) benzamide (KU-54), an antiulcer drug, on the tissue respiration of the gastric mucosa and the liver were studied in rats. Oral KU-54 at 100 mg/kg twice daily for 5 days (though it was given only once on the 5th day) caused an increase in oxygen consumption of the gastric mucosa in rats, but did not affect that of the liver. Thus the principal active site of KU-54 on tissue respiration was found to be the gastric mucosa. Oral KU-54 at 100 mg/kg once daily for 11 days significantly accelerated the oxygen consumption of marginal gastric mucosa of acetic acid ulcer in rats. The effect of oral gefarnate at 200 mg/kg was about half that of KU-54 at 100 mg/kg, but it was not significant. In addition, oral KU-54 at 100 mg/kg twice daily for 5 days (though it was given only once on the 5th day) significantly inhibited the decrease of oxygen consumption of the gastric mucosa in hemorrhagic shocked rats. The effect of oral gefarnate at 100 mg/kg was not like that at KU-54 at 100 mg/kg in conscious rats. When KU-54 was added in the incubation medium with small gastric mucosal fragments of rats, the increase of oxygen consumption of the gastric mucosa did not occur. Oral KU-54 at 100 mg/kg significantly accelerated a glycogen consumptive stimulation of the gastric mucosa of the corpus in ischemic rats, but the respiration of the antral mucosa was not accelerated under anaerobic incubating conditions. Oral gefarnate at 200 mg/kg accelerated an anaerobic glycolysis of the gastric antral mucosa in rats.