Allergic esophagitis (AE) is an inflammatory disorder of the esophagus characterized by lack of response to medical and surgical anti-reflux therapies, normal esophageal pH recording, distinctive mucosal histopathology, and response to anti-allergic treatments (Am J Surg Pathol, 1999;23:390-6). Dysphagia and food impaction occur frequently, despite the absence of stricture, and resolve with medical therapy. The pathophysiology of this dysphagia is unknown but may relate to reversible changes in the esophageal wall. High-resolution probe endosonography (HRPE) provides detailed radial imaging and permits real-time measurement of individual layers of the esophageal wall.We have applied HRPE to investigate changes in children with AE and report our initial findings. Methods: Children with AE and control children without esophagitis were enrolled for study. The Olympus EU-M30 ultrasound processor and 20 MHz miniprobe were utilized. Probes were passed through the operating channel of a gastroscope at the time of diagnostic endoscopy. Small amounts of water were infused into the esophageal lumen for acoustic coupling. Duplicate real-time measurements (0.1mm resolution) of the esophagus were obtained with the probe tip positioned 3-5 cm above the lower esophageal sphincter and with the esophagus in a non-contracted state. Measurements were taken from areas of maximal thickness where all of the echo layers could be clearly distinguished and included thickness of the total wall (tw), combined mucosa and submucosa (m/sm), and muscularis propria (mp). Comparisons were made with control patients without esophagitis. The Mann-Whitney test was used for non-parametric statistical analysis of mean values. Results: Eight children with AE (mean age, 10.1 ± 5.2yr) were compared with four control children (mean age, 7.8 ± 6.3yr)(p=0.396). Seven echo layers were seen in all patients. Echo layers were significantly thicker in AE patients compared with control patients. Mean tw thickness was 2.2 ± 0.1mm (control) compared with 2.8 ± 0.7mm (AE)(p=0.035). Mean m/sm thickness was 1.1 ± 0.2mm (control) versus 1.6 ± 0.4mm (AE)(p=0.017). Mean mp thickness was 1.0 ± 0.1mm (control) compared with 1.3 ± 0.3mm (AE)(p=0.025). Conclusion: HRPE identifies significant thickening of the mucosa/submucosal and muscle layers of esophageal wall in children with allergic esophagitis compared to normal controls. This thickening may contribute to the observed dysmotility in these patients.