BACKGROUND: Functional dyspepsia is characterized by upper abdominal pain or discomfort. AIM: To assess the benefit of the 5-HT3-receptor antagonist alosetron in a pilot, dose-ranging, placebo-controlled, multicentre, randomized clinical trial. METHODS: A total of 320 functional dyspepsia patients received placebo (n=81), or alosetron 0.5 mg b.d. (n=77), 1.0 mg b.d. (n=79) or 2.0 mg b.d. (n=83) for 12 weeks, followed by 1 week of follow-up. Primary efficacy was the 12-week average rate of adequate relief of upper abdominal pain or discomfort. Secondary endpoints assessed pain and upper gastrointestinal symptoms. RESULTS: Twelve-week average rates of adequate relief of pain or discomfort were 46% (95% CI: 37-54%), 55% (95% CI: 46-63%), 55% (95% CI: 47-64%) and 47% (95% CI: 38-55%) in the placebo, 0.5 mg, 1.0 mg and 2.0 mg alosetron groups, respectively. Alosetron 0.5 mg or 1.0 mg showed potential benefit over placebo for early satiety and postprandial fullness. Females showed greater responses compared to males. Patients with adequate relief had significantly (P < 0.001) greater reductions in severity and frequency of functional dyspepsia symptoms than those without adequate relief. Constipation was the most commonly reported adverse event. CONCLUSIONS: Alosetron showed potential benefit in relieving functional dyspepsia symptoms compared to placebo. Patients with adequate relief of upper abdominal pain or discomfort showed improvements in multiple functional dyspepsia symptoms.