BACKGROUND: From a clinical perspective, the regurgitation of the gastric contents above the upper esophageal sphincter has greater clinical relevance than gastroesophageal reflux. The authors investigated the incidence of regurgitation of gastric contents above the upper esophageal sphincter associated with the laryngeal mask airway(LMA) and the endotracheal tube(ETT) by methylene blue(50mg) gelatine capsule and pH probe in positive pressure ventilated patients during long surgical procedures . METHODS: Sixty patients scheduled for elective orthopedic surgery with a standardized general anesthetic technique were randomly allocated to receive either a LMA(n=34) or a ETT(n=26) for airway management. For the detection of regurgitation episodes during anesthesia, a pH monitoring probe was positioned in the hypopharynx 30 minutes before induction and a methylene blue capsule was swallowed just before induction. At the end of anesthesia, the episodes of regurgitation of gastric contents above upper esophageal sphincter were analyzed according to the pharyngeal blue staining or pH< or =4. RESULTS: There were no episodes of regurgitation of gastric contents(pH< or =4 or/and methylene blue staining) above the upper esophageal sphincter detected during the course of measurement. There was no clinical evidence of aspiration in either group. CONCLUSIONS: In comparison with ETT, the use of LMA does not appear to result in increased incidence of regurgitation of gastric contents above upper esophageal sphincter in positive pressure ventilated patients during long surgical procedures.