To evaluate the effects of gastric intramural pH on intraluminal fluid of stomach during halothane anesthesia, the pH of gastric content and the gastric intramural pH measured by noninvasive method under halothane anesthesia were compared with those during epidural anesthesia. Nineteen patients without gastrointestinal disorders who received elective surgery were studied; 14 patients were anesthetized with N2O-O2-halothane and 15 patients were anesthetized with N2O-O2, flunitrazepam and lumber epidural anesthesia. The intramural pH was calculated from the Henderson-Hasselbalch's equation: intramural pH = 6.1 + ([HCO3-]/PCO2 X 0.0307), substituting [HCO3-] in arterial blood for [HCO3-] in tissue and PCO2 in gastric content for PCO2 in tissue. The pH of gastric content was elevated gradually under halothane anesthesia, but it was unchanged under epidural anesthesia. On the other hand the intramural pH was unchanged during both anesthetic methods and there were no significant differences between the two groups. These results suggest that the elevation of the pH of gastric content under halothane anesthesia is not the result of intragastric microcirculatory impairment and halothane may have other suppressive actions on gastric acid secretion.