BACKGROUND: There were several studies for the incidence of gastroesophageal reflux associated with the laryngeal mask airway(LMA), but the results of those studies were much different from one another. The authors of this study measured the intraesophageal pH at 5cm above lower esophageal sphincter(LES) to compare the incidence of gastroesophageal reflux associated with the LMA and the endotracheal tube(ETT) in positive pressure ventilated patients during long surgical procedures. METHOD: Ninety patients scheduled for elective orthopedic surgery with a standardized general anesthetic technique were randomly allocated to receive either a LMA(n=49) or a ETT(n=41) for airway management. The esophageal manometry was carried out for the exclusion of esophageal motility disorders and a probe with a pH electrode was passed nasally into the esophagus and positioned at 5 cm above LES one day before the operation. After that, recordings of pH for the diagnosis of gastroesophageal reflux disorder and for the detection of reflux episodes during and immediate after anesthesia were performed. RESULTS: There was no significant difference in the incidence of reflux(pH< or =4) between groups; only two patients in LMA and three patients in ETT had reflux episodes in the removal or arousal phase. All of them had experiences such as a coughing or straining during those phases. There was no clinical evidence of aspiration of gastric contents in either group. CONCLUSION: In comparison with ETT, use of LMA does not appear to result in increased incidence of reflux in positive pressure ventilated patients during long surgical procedures.