Fourteen patients with chronic bronchopulmonary disease and suspected of having gastroesophageal reflux were studied for 16 hr by intraesophageal pH monitoring to investigate the effect of the prokinetic drug cisapride. Cisapride was administered orally in a double-blind cross-over study. The initial dose was 0.3 mg/kg, followed by 0.15 mg/kg every 4 hr for 12 hr. Cisapride was shown to be superior to placebo in reducing gastroesophageal reflux. Both during the total recording period and during the sleep period, cisapride significantly decreased the percentage of time during which the pH was 4 or less (vs placebo; total period, -60%; sleep, -80%) and reduced the number of reflux spells of at least 5 min (-64%; -92%). No adverse effects of cisapride were observed.