OBJECTIVE: Therapeutic trials in functional dyspepsia consistently show a substantial placebo response, but there is no clear explanation for such an effect. Our aim was to evaluate symptomatic, gastrointestinal motor, and gastric sensorial responses to placebo treatment in patients with chronic and severe functional dyspepsia who were part of a therapeutic trial. METHODS: Thirty patients were treated during 8 wk with placebo (white-colored 8-mm tablets containing cellulose) by mouth, 20 min before breakfast, lunch, and dinner. We quantified the symptomatic response to placebo as a change in global health status, and also as a change in the individual and combined (global symptom index) of a five-symptom complex: upper abdominal pain, nausea, vomiting, bloating/fullness, and early satiety. Gastroduodenal motility, during fasting and postprandially, was evaluated by manometry in all patients pretreatment and in 17 patients posttreatment. Gastric sensitivity to distension was evaluated in 18 patients pretreatment and in five patients posttreatment (all of them clinical responders). RESULTS: Placebo treatment produced a striking symptomatic improvement; by 8 wk 80% of the patients reported an improved global health status and their global symptom index markedly decreased (23.9+/-1.3 pretreatment vs 9.1+/-1.2; p < 0.05). Placebo increased the number of gastric phases III starting in the antrum during the fasting period (1.1+/-0.1 vs 1.6+/-0.2; p < 0.05). As a group, no significant changes in postprandial gastroduodenal motility were observed after placebo treatment. However, after placebo a significant improvement in the antral motility index (MI) was observed in the subset of patients with antral hypomotility (MI pretreatment: 7.9+/-1.0; MI posttreatment: 11.7+/-0.4; p < 0.05). Before placebo treatment, patients with functional dyspepsia showed increased sensitivity to stepwise distension of the stomach relative to healthy individuals. After 8 wk of placebo treatment sensitivity to distension remained unchanged, even though patients' clinical status was markedly improved. CONCLUSION: In patients with functional dyspepsia, the symptomatic response to placebo is substantial. Some significant changes were also observed in gastric motility: increase in the gastric phase III number as well as in the postprandial antral motility index in those with hypomotility pretreatment. Remarkably, however, clinical improvement seems to occur independently of detectable changes in gastroduodenal motor activity or gastric hypersensitivity to distension.