To determine the value of pH testing in clinical practice in gastroesophageal reflux disease patients who failed anti-reflux treatment. Patients resistant to standard dose proton pump inhibitor or an H2-blocker underwent pH testing. Randomly selected patients from the proton pump inhibitor failure group underwent the modified acid perfusion test as compared to patients with non-erosive reflux disease. In the proton pump inhibitor failure group (n = 70), 63.8% had a normal pH test as compared to 29% in the H2-blocker group (n = 31) (P = 0.007). Sensory intensity rating and acid perfusion sensitivity score were significantly higher in the non-erosive reflux disease control group than the proton pump inhibitor failure group (P < 0.05). Most patients who continued to be symptomatic on proton pump inhibitor once daily demonstrated a normal pH test and overall lack of increased chemoreceptor sensitivity to acid.