Thirty-six patients aged 15-74 with palatal dental erosion where the aetiology was unclear were investigated for gastro-oesophageal reflux. Ten subjects without symptoms of reflux or palatal erosion acted as controls. Distal and proximal oesophageal reflux were measured over 24 hours by dual channel antimony electrodes. Oral pH was measured simultaneously over the same period by a radio-telemetry capsule held palatally in a vacuum formed splint. Data were logged onto two portable digitable recorders. Twenty-three patients (64%) with palatal erosion had pathological gastro-oesophageal reflux compared with standard criteria. More than 4% of the total percentage time that the pH is less than 4 in the distal oesophagus is internationally recognised by gastroenterologists as representing a pathological level of reflux. The median percentage time < pH 4 in the distal oesophagus for these patients was 5.7%, in the proximal oesophagus, pH 4 was 0.5% and pH < 5 was 3.1%. In the mouth, the results for the percentage time that the pH < 5.5 was 0.3% and < 6 was 4.4%. A relationship was observed between the pH < 4 in the distal oesophagus and the mouth pH < 5.5 (r = 0.47, P = 0.002) and pH < 6 (r = 0.34, p = 0.02). There was a relationship between oral acid exposure time pH < 6 and the tooth wear index (r = 0.37, P = 0.01). These results show that gastro-oesophageal reflux is strongly associated with palatal erosion and that some patients presenting with palatal dental erosion should be assessed for gastro-oesophageal reflux as a possible cause, even in the absence of clinical symptoms of reflux.