A new automated suction device has been developed to aspirate the contents of the distal oesophagus to monitor the constituents of the refluxate in patients with gastro-oesophageal reflux disease. Using antimony and glass electrodes with solid-state pH recorders it has been conclusively shown that gastric acid is responsible for the mucosal damage seen in reflux oesophagitis but new evidence is emerging that other constituents of the gastroduodenal juice, in particular bile acids, are also damaging to the oesophageal mucosa. The main difficulty lies in that there is no reliable method of monitoring this component of the refluxate except by direct aspiration of the contents for assay. This new technique of oesophageal sampling utilizing a software-controlled suction process with simultaneous pH recording has helped to identify patients at risk of refluxing potentially harmful substances and is a valuable addition to the armamentarium of investigative procedures for patients with gastro-oesophageal reflux disease.