PD, the electrical potential difference across the gastric mucosa, is a variable used frequently in experimental studies. Existing methods for PD measurements are, however, unstable, and variations in the pH of the gastric juice causes liquid junction potentials between gastric juice and the PD measuring probe. A new PD measuring system has been developed with high stability, easy handling, and correction for the liquid junction potentials. PD was measured between a stomach microelectrode and an intravenous reference electrode connected to a millivoltmeter. pH was measured by an intragastric microelectrode. The liquid junction potential was calculated by using the pH measured in the gastric juice and the Henderson equation and was then subtracted from the measured PD to provide a better approximation of the PD across the mucosa. The liquid junction potential calculated as stated above correlated with the liquid junction potential calculated from precise ion determinations made in gastric juice samples (y = x; r = 0.92; p less than 0.05). The reliability of the PD measuring system was tested in vitro and in vivo and was satisfactory. In conclusion, a new, reliable, and easily applied method for gastric PD measurements corrected for the liquid junction potential between gastric juice and the PD measuring probe has been developed.