OBJECTIVE: To determine the diagnostic value of empirical treatment with omeprazole in the diagnosis of gastroesophageal reflux disease (GERD). METHODS: Patients with symptoms suggestive of GERD underwent upper gastrointestinal endoscopy and 24-h esophageal pH monitoring. Patients with reflux esophagitis grade 0 or 1 were included in the study and were randomized to double-blind treatment with either 40 mg omeprazole or placebo o.m. The effect of treatment was evaluated after 1 and 2 wk with a symptom questionnaire with a four-grade Likert scale, and symptomatic response outcome was compared with the results of 24-h pH-metry. RESULTS: Ninety-eight patients were included; however, 13 were excluded from the final analysis because of protocol violation. Of the remaining 85 patients, 54 had no signs of esophagitis at endoscopy, and 31 had esophagitis grade 1. The pH registration showed pathological gastroesophageal reflux in 47 patients (55%). Forty-one patients were randomized to treatment with omeprazole and 44 to placebo. There was a significant correlation between the pH registration result and response to omeprazole (p = 0.04, chi2), but not to placebo (p = 0.16). With pH-metry as the gold standard, the omeprazole test had positive and negative predictive values of 68% and 63%, respectively, for the diagnosis of GERD. When the omeprazole test was used as the gold standard, the positive and negative predictive values of pH monitoring were 68 % and 63 %, respectively. Similar sensitivity was found when the pH-metry was compared with presence of esophagitis. CONCLUSION: Determination of the symptomatic response to 40 mg of omeprazole for 14 days is a simple and inexpensive tool for the diagnosis of GERD, with a sensitivity and specificity comparable to 24-h pH monitoring.