To compare reflux events detected by intraesophageal pH monitoring with that of scintigraphy, we simultaneously performed both techniques along with esophageal manometry in nine patients with severe reflux esophagitis. Two hundred eighteen reflux events were detected in the recumbent posture after a meal during a 40-min interval. Both techniques simultaneously detected only 23% of all reflux events. Scintigraphy alone detected 61% of all reflux events as opposed to 16% for pH monitoring. Of those reflux events diagnosed only by scintigraphy, more occurred while the intraesophageal pH was less than 4 (ie, during an acid-clearing interval) than while the intraesophageal pH was greater than 4 (ie, when intragastric contents were neutralized by the meal). Most reflux events occurred during periods of stable, but low LES pressure. While reflux events diagnosed by scintigraphy significantly decreased during the second of two 20-min postprandial intervals, those by pH monitoring tended to increase. That simultaneous scintigraphy and pH monitoring agreed on less than 1/3 of all reflux events not only underscores the fact that both techniques measured different physical components of the esophageal refluxate (ie, volume vs acid concentration, respectively), but also were influenced by different physiologic events such as the ingestion of a meal, gastric emptying, and esophageal acid clearance.