BACKGROUND/AIMS: To evaluate the value of a 2-week high dose proton pump inhibitor (PPI) treatment on patients with overlapping non-erosive gastroesophageal reflux disease (NERD) and functional dyspepsia (FD). METHODS: Sixty overlapping NERD and FD patients with symptom onset > 3 months prior underwent 24-hour esophageal pH monitoring studies. All patients received rabeprazole 20 mg b.i.d. for 2 weeks. The reflux and dyspeptic symptoms were evaluated using a symptom questionnaire with 4-point Likert scales before and at the end of treatment. A positive PPI test was defined as score improvement in ≥ 50% from the baseline in the typical reflux symptoms. RESULTS: The prevalence of each reflux and dyspeptic symptom did not differ significantly between patients with positive and negative pH tests. After the PPI treatment, epigastric burning, acid regurgitation, heartburn, nausea, vomiting and chest discomfort scores were significantly improved compared to pretreatment values (P < 0.05), whereas postprandial abdominal fullness, early satiation, belching and food regurgitation were not. The proportion of patients who responded to the PPI treatment did not differ significantly between patients with positive and negative pH tests. The sensitivity, specificity, PPV, NPV and accuracy of 2-week high dose rabeprazole treatment for diagnosing gastroesophageal reflux disease were 47%, 38%, 50%, 35% and 43%, respectively. CONCLUSIONS: The two-week high dose PPI treatment was not effective for early satiation, postprandial abdominal fullness, regurgitation or belching symptoms in patients with overlapping NERD and FD. Acid exposure in the distal esophagus could not predict the response of symptoms to PPI. In addition, the 2-week PPI test provided limited value for gastroesophageal reflux disease diagnosis in patients with overlapping NERD and FD.