Totally isolated canine stomachs, perfused with homologous blood, were used for the study of potentiation between pentagastrin and histamine. These stimulants were infused into the gastric arterial system separately, or combined. Gastric secretion and perfusion blood were sampled every 30 min for biochemical analyses Combination of pentagastrin plus histamine gave significantly higher outputs of HCl than could be accounted for on the basis of summation of stimulatory effects. True potentiation, with regard to gastric juice volume and HCl output, occurred when two stimuli were infused simultaneously. Gastric hypersecretion of H+ was associated with increased O2–consumption by the stomach and by the alteration of the physiological relationship between the pH of arterial and venous blood sampled from gastric vessels. It was concluded that the totally isolated canine ex vivo stomach, perfused with homologous blood, is a suitable experimental preparation for the study of potentiation effects between two humoral gastric secretagogue