BACKGROUND: Oesophageal clearance of acid reflux consists of an initial volume clearance followed by neutralisation of the acidified mucosa by swallowed saliva (chemical clearance). Ineffective oesophageal motility (IOM), a frequent finding in patients with gastro-oesophageal reflux disease (GORD), has been claimed to underlie prolonged acid clearance by affecting oesophageal emptying and saliva transport. Intraluminal impedance allows non-radiological monitoring of movement of oesophageal liquids. AIMS: To evaluate the relevance of IOM during oesophageal volume and chemical clearance using combined pH impedance measurements. SUBJECTS: Impedance was validated with fluoroscopy to study volume clearance in three healthy subjects. Acid clearance tests were performed in 10 healthy subjects in the upright and supine positions, before and after oesophageal peristaltic disruption with sildenafil 50 mg. METHODS: After instillation of an acid bolus, simultaneous manometry, pH, and impedance were used to study oesophageal motility, chemical clearance, and volume clearance, respectively. RESULTS: Impedance allowed assessment of volume clearance accurately, showing a strong correlation with fluoroscopy (r(2)=0.89). Sildenafil provoked a graded impairment in oesophageal motility in healthy subjects without affecting saliva secretion. In the upright position, volume clearance was slightly prolonged only with severe IOM (>80% abnormal peristaltic sequences). In the supine position, severe IOM significantly prolonged chemical and volume clearance. Moderate IOM (30-80% abnormal peristalsis) had no effect. With normal peristalsis and moderate IOM, clearance times were similar in the upright and supine positions. Severe IOM however had a greater impact on clearance in the supine than in the upright position. CONCLUSION: Ineffective oesophageal motility has little effect on oesophageal clearance during upright acid reflux. With supine reflux, only severe IOM is associated with prolonged oesophageal clearance.