This investigation used a high-frequency intraluminal ultrasound (HFIUS) probe to study changes in esophageal muscle thickness as a marker of muscle contraction. The aim of this study was to determine whether this technique could accurately measure distention of the esophagus during swallows of liquid bolus and during gastroesophageal reflux (GER) in normal subjects. Despite some limitations, HFIUS appears to be a valid technique for both of these measurements in normal subjects. Future studies in patients with symptomatic GER disease (GERD) should be able to determine whether typical symptoms such as heartburn, as well as atypical symptoms such as chest pain, are related to the GER-related distention of the esophagus.