Recent studies have emphasized the role of concealed accessory pathways in reciprocating supraventricular tachycardia. Diagnosis has generally required multicatheter electrophysiologic study. We recorded esophageal electrograms during study in 16 patients with reciprocating tachycardia due to reentry using an accessory atrioventricular pathway, and in 12 patients with reciprocating tachycardia due to reentry in the AV node. The interval from onset of ventricular depolarization to earliest atrial activation (V-AMIN), earliest atrial activity on the esophageal lead (V-AESO), and high right atrium (V-HRA) was measured. No patient with RT due to an accessory atrioventricular pathway had a V-AMIN or V-AESO less than 70 ms, or a V-HRA less than 95 ms. In contrast, 11 of 12 patients with reentry in the AV node had V-AESO intervals less than 70 ms. Esophageal recording during reciprocating tachycardia provides a simple screening procedure available to all practicing physicians to exclude the diagnosis of accessory atrioventricular pathways in the genesis of paroxysmal supraventricular tachycardia.