We have measured the effect of pneumoperitoneum and the Trendelenburg position on lower oesophageal sphincter (LOSP) and barrier pressures (BrP) in 11 anaesthetized pigs while measuring the incidence of gastro-oesophageal reflux with a pH electrode. Propofol in combination with sufentanil had no effect on LOSP or BrP. Adoption of the Trendelenburg position with a pneumoperitoneum of 15 mm Hg resulted in a significant increase in LOSP (P < 0.002) and BrP (P < 0.001). However, in two of 11 pigs who had the lowest LOSP before induction, there was regurgitation.