The effect of the new prokinetic drug cisapride on the resting lower oesophageal sphincter pressure and on the strength of peristaltic contractions was studied in 10 healthy controls and in 10 reflux patients with abnormally low (less than 10 mm Hg) basal lower oesophageal sphincter pressure. A slow intravenous injection of cisapride 10 mg significantly increased the sphincter pressure in the controls but even more in the patients in whom it almost doubled the resting lower oesophageal sphincter pressure of 8.7 (0.5) mm Hg to between 15 and 20 mm Hg for at least 90 min. Results are expressed as mean (SE). Cisapride also significantly increased the amplitude of peristaltic contractions in controls and reflux patients. Therefore, cisapride might be useful in the treatment of reflux.