BACKGROUND: The role of acid in functional dyspepsia is controversial and drug treatment trials indicate that only a subset of patients has acid-related symptoms. A novel single-subject trial design, the Random Starting Day trial (RSD trial), was developed to identify acid-related symptoms. We hypothesized that RSD trial responders and non-responders would react differently to gastric acid stimulation. Development of epigastric pain was expected in RSD trial responders after pentagastrin stimulation during placebo treatment, but not during omeprazole treatment. In non-responders, epigastric pain was expected not to be influenced by gastric acid stimulation or type of treatment. METHODS: Nineteen patients were evaluated. Symptomatic response to pentagastrin (6 microg/kg) was assessed twice in each patient following placebo and omeprazole (40 mg bid) treatment in a randomized, double-blind, cross-over design. Epigastric pain was assessed every 15 for 90 min after stimulation using a 5-graded Likert scale and a VAS scale. A positive acid provocation test was defined as an increase of the Likert score of epigastric pain by at least one grade after pentagastrin stimulation during placebo treatment but not during omeprazole treatment. RESULTS: The acid provocation test was positive in 43% (3/7) of responders compared to only 17% (2/12) non-responders. VAS-score changes showed trends towards a more pronounced symptom reduction during omeprazole treatment in responders compared to non-responders. CONCLUSION: Patients identified as having acid-related dyspepsia more often developed epigastric pain following acid stimulation during placebo and not during omeprazole treatment. Due to the low sample size the difference was not considered significant.