The acid perfusion test (APT) is a test of esophageal acid sensitivity. In gastroesophageal reflux disease (GERD), the APT has largely been superseded by indexes derived from 24-hr esophageal pH monitoring: symptom index (SI), symptom sensitivity index (SSI), and symptom association probability (SAP). To evaluate the role of APT in patients with GERD we compared values of SI, SSI, and SAP in 126 APT+ and 146 APT- patients. Median values for SI, SSI, and SAP were higher in the APT+ compared with the APT- group (P < 0.001). More patients had a positive SI, SSI, and SAP in the APT+ compared with the APT- group (SI, P < 0.0001; SSI and SAP, P < 0.001). Patients with a negative APT were unlikely to have symptoms caused by acid reflux (negative predictive value, 86%). APT may be useful in detecting acid sensitivity in patients who do not report symptoms on 24-hr esophageal pH monitoring.