The effect of cisapride, a new gastrointestinal prokinetic drug, on oesophageal motility and acid reflux was studied in 14 children with gastro-oesophageal reflux disease, receiving either placebo or cisapride 0.15 mg/kg intravenously. Cisapride significantly (p less than 0.01) increased the lower oesophageal sphincter pressure (+124%), the amplitude (+84%) and duration (+24%) of oesophageal peristaltic waves, whereas the placebo treatment did not produce any changes. Subsequently, all 14 children underwent 24 hour oesophageal pH-monitoring before and after four weeks of treatment with oral cisapride 0.2 mg/kg tid given in addition to postural therapy and thickened feedings. The 24 hour intraoesophageal pH recordings and symptomatic scores were compared with those of 10 control patients treated only by postural therapy and thickened feedings. When compared with baseline pH data, cisapride significantly reduced the oesophageal acid exposure time, the mean duration of each reflux episode, the duration of the longest reflux episode and the number of long lasting reflux episodes; the number of reflux episodes was not influenced. The effect of cisapride was marked and consistent during fasting and sleep periods. Oesophageal acid exposure was reduced more significantly in patients given cisapride (-61%) than in controls (-24%; p less than 0.001). Symptom improvement was greater after four weeks of cisapride treatment (score reduction: 61%) than after postural and dietary therapy alone (score reduction: 42%; p less than 0.01). No adverse effects occurred. These findings suggest that cisapride is a valuable drug in the management of gastro-oesophageal reflux disease in children.