Background: Recent advances in the assessment of oesophageal function include high resolution manometry and ambulatory impedance-pH monitoring. These have improved our understanding of the pathophysiology of gastro-oesophageal reflux disease including the importance of components other than acid in the gastrooesophageal reflux ate. Aims: 1: Provide evidence of gastro-oesophago-pharyngeal reflux in patients diagnosed with extra-oesophageal reflux disease.2: Investigate the presence of pepsin in saliva in health and disease.3: Investigate the changes in gastrooesophageal motility and reflux in patients undergoing sleeve gastrectomy. Methods: High resolution oesophageal manometry was used to assess oesophageal peristalsis, upper and lower oesophageal sphincters. Ambulatory impedance-pH monitoring was used to determine the physical and chemical properties of gastrooesophageal and gastro-oesophago-pharyngeal refluxate. The presence of pepsin in saliva was detected by indirect sandwich ELISA. Gastric emptying was measured ) with a 13C labelled octanoic acid breath test. Results: 1. Approximately half of all patients diagnosed with gastro-oesophagopharyngeal reflux had evidence of pharyngeal acid or non-acid reflux. These patients were more likely to have detectable levels of pepsin in their saliva. 2. Pepsin can be detected in saliva, preceded by reflux events in health and disease. 3. After sleeve gastrectomy there is increased acid and non-acid gastro-oesophageal reflux with changes in lower oesophageal sphincter pressure and gastro-oesophageal pressure gradient. Conclusion: 1. Targeting patients with objective evidence of gastro-oesophagopharyngeal reflux for anti-reflux therapy may help to improve treatment outcomes. 2. Detection and quantification of pepsin in saliva may be a useful screening tool for patients with suspected gastro-oesophageal reflux. 3. Reduction in the lower oesophageal sphincter pressure and an increase in gastro-oesophageal pressure gradient following sleeve gastrectomy are associated with significant gastrooesophageal reflux.