The effects on lower oesophageal sphincter tone of intravenous ranitidine 150 mg followed by atropine 0.6 mg were studied in six healthy volunteers. Ranitidine increased the mean lower oesophageal sphincter pressure by 21.2 cm H2O (p less than 0.01). Subsequent injection of atropine lowered the lower oesophageal sphincter pressure but not significantly, mean sphincter pressure remaining 14.2 cm H2O above control. Barrier pressure to reflux (lower oesophageal sphincter pressure minus gastric pressure) increased significantly after intravenous ranitidine injection, and although it fell after intravenous atropine it was still above control levels. The results of this study suggest that ranitidine increases lower oesophageal sphincter tone. When it is given prior to atropine injection within 20 minutes before induction of anaesthesia it counteracts the deleterious effect of the latter on sphincter tone and barrier pressure to reflux.