Oesophageal transmural potential difference measurements have been used to localize the oesophagogastric mucosal junction and to detect reflux-induced mucosal damage. The current study confirms that such measurements lead to reproducible results when they are used to identify the oesophagogastric mucosal junction. In normal persons this anatomical structure is always localized within or below the lower oesophageal sphincter. In contrast potential difference measurements of the distal oesophagus show marked intraindividual variations and no correlation was found between these measurements on 2 different days. These results indicate that potential difference measurements are a valuable tool to determine the relation of the oesophagogastric mucosal junction to the lower oesophageal sphincter, but are less useful for detecting oesophageal mucosal alterations.