In recent years, there has been renewed interest in preoperative methods to reduce gastric acidity, thus lessening the risk of a serious pulmonary reactions following aspiration of gastric contents. Emergency obstetrical patients frequently have large volumes of gastric fluid. It is less commonly appreciated that patients fasting prior to elective surgery afterive in operating room with large gastric fluid volumes with a low pH. Prophylactic preoperative oral administration of antacids has been shown to reduce preoperative gastric acidity in significant percentage of patients, but aspiration of antacids can be associated with pulmonary complications, and there use may be associated with increased gastric volume. Preoperative adrpinistration of glycopyrrolate may decrease the frequency of surgical patients with a low gastric pH, and it appears that the volume of gastric fluid may be reduced by medication that relax the pylorus. However, none of these pharmacologic manuevers completely abolisbes the possibility of serious pulmonary damage with aspiration. Mendelson and Teabeat demonstrated the importance of pH in the etiology of acid aspiration and it is generally accepted that the critical pH is 2. 5 or less, i.e. the risk of aerious pulmonary reaction increases progressively as the pH of the aspirate falls below 2.5. A critical volume of acid aspirate is also necessary for widespread pulmonary damage to occur irrespective of a low gastric pH. The critical volume is rhesus monkeys has been shown to be 0.4 ml/kg, but the critical volume in man is less well difined. Several investigators have determined the patient to be at risk of serious pulmonary complications with aspiration if at least 25 ml of gastric fluid with a pH of 2.5 or less is aspirated. The present study was undertaken to investigate the effects on the volume and pH of gastric juice under general anesthesia. The 35 patients were studied, and were divided. into 4 group account to the kind of premedicants, N.P.O. time, weight, and obstetric patients Gastric juice, aspirated through a Levine tube, was examined for pH and. volume under general anesthesia.