The effect of a meal on the rate of transient lower esophageal sphincter (LES) relaxations and patterns of gastroesophageal reflux was investigated in 49 patients referred for evaluation of gastroesophageal reflux. Esophageal motility and pH were recorded concurrently before and after a standard meal. In the patients with symptomatic reflux, the meal induced a four- to sevenfold increase in the gastroesophageal reflux through two mechanisms: a four- to fivefold increase in the rate of transient LES relaxations and an increase in the proportion of transient LES relaxations accompanied by reflux from 47% to 68%. Overall the rate of reflux episodes that occurred by mechanisms other than transient LES relaxation did not increase significantly. An exception to these findings were those in six patients with chronically absent basal LES pressure in whom transient LES relaxations could not be scored. In these patients, reflux increased postprandially through mechanisms other than transient LES relaxation. These findings confirm the pivotal importance of transient LES relaxations in the pathogenesis of gastroesophageal reflux.