Fasting antral area was examined by ultrasonography in 40 healthy subjects and in 106 patients with non-ulcer dyspepsia (NUD) and erosive prepyloric changes (EPC) before and after treatment with cisapride or placebo. The patients were examined twice, first after a run-in period of 14 days of placebo and then after 14 days of cisapride, 10 mg three times daily, or placebo. The relaxed width of the antral area was measured in two sections: a vertical section in which the antrum, the superior mesenteric vein, and the aorta were visualized simultaneously, and a horizontal section that included the pylorus and the middle of the antrum up to 5 cm proximal to the pylorus. The mean antral area was wider (p less than 0.001), both in vertical and horizontal sections, in patients with NUD and EPC than in controls. The antral area in NUD patients was wider (p less than 0.05) in smokers than in non-smokers. The area tended to decrease during treatment with cisapride (p = 0.08). Bloating was the only symptom significantly associated with a wide antral area (p = 0.01). The results suggest a relationship between a wide fasting antral area and NUD with EPC.