Esophageal function was evaluated in 51 children less than 2 years of age with radiologic evidence of gastroesophageal reflux. Detection of an acid esophageal pH was a sensitive measure of gastroesophageal reflux. Lower esophageal sphincter pressures were greater in reflux patients with respiratory symptoms (18.0 ± 1.4 mm Hg) than in reflux patients without respiratory symptoms (9.5 ± 1.0 mm Hg). The intra-abdominal segment of the lower esophageal sphincter was shorter in patients with reflux than in controls (0.51 ± 0.05 cm vs. 0.75 ± 0.08 cm). It was also shorter in patients requiring surgical therapy (0.34 ± 0.05 cm) than in those responding to medical therapy (0.63 ± 0.07 cm).