BACKGROUND Disordered gastric antral motor activity may be induced by mental stress. The effect of cisapride on these abnormalities has previously not been investigated. METHODS Ten healthy subjects and 19 patients with functional dyspepsia (FD) and erosive prepyloric changes participated in the study. Antral motility was recorded with real-time ultrasonography after ingestion of 500 ml meat soup during i) a 4-min rest period, ii) 2.5 min of mental stress, and iii) a 4-min recovery period. Patients and controls were studied after 3 days of treatment with 10 mg cisapride three times daily and placebo in a double-blind crossover design. RESULTS Mean postprandial amplitude of antral contractions was lower in patients than controls (p < 0.001). Antral amplitude was reduced by mental stress in healthy persons (p < 0.001) but not in patients. Both fasting and postprandial antral areas were larger in FD patients than controls (p < 0.001 and p = 0.02, respectively). Cisapride reduced the fasting (p < 0.001) and the postprandial (p = 0.05) antral area in the FD group but not in controls. The soup meal produced dyspeptic symptoms in 90% of the patients and in only 10% of the controls (p < 0.001). Cisapride had no significant effect on symptoms or antral contractions. CONCLUSIONS Mental stress induced antral hypomotility in healthy subjects but not in patients with FD who had reduced motility at base line. Cisapride reduced the enlarged fasting and postprandial antral areas in the patients but had no effect on amplitudes of antral contractions or symptoms.