Gastro-oesophageal reflux disease is defined as the presence of symptoms or lesions that can be attributed to the reflux of gastric contents into the oesophagus. Aspiration and prolonged monitoring studies in humans have shown that reflux of gastric contents is comprised of both acid and non-acid components, in healthy as well as diseased people. Methods to monitor the non-acid component of the refluxate are described in detail. Experimental models suggest that synergism between acid and pepsin and conjugated bile acids have the greatest damaging potential for oesophageal mucosa, although unconjugated bile acids may be caustic at a more neutral pH. Human studies are compatible with a synergistic action between acid and duodenogastric reflux in inducing lesions. During prolonged monitoring studies, typical gastro-oesophageal reflux disease symptoms are more related to acid reflux events than to non-acid reflux events. However, symptoms that persist during acid-suppressive therapy are often related to non-acid reflux events. The therapeutic options for the non-acid component of the refluxate, including acid suppression, prokinetics, baclofen and surgery, are discussed.