Transesophageal atrial pacing (TAP) is used in the diagnosis and treatment of paroxysmal narrow QRS complex tachycardia (NQT). The aim of this study was to assess the value of this technique in predicting the efficacy of antiarrhythmic therapy. The study group consisted of 30 consecutive patients with spontaneous NQT whose clinical tachycardia was inducible by TAP. Baseline TAP was performed off all antiarrhythmic medication and repeated during oral antiarrhythmic drug therapy. The pacing protocol consisted of three stages: a single extrastimulus introduced at progressively shorter coupling intervals during sinus rhythm, pacing at incremental rates to the point of second-degree AV block, and bursts of rapid pacing. On repeat stimulation while on oral antiarrhythmic therapy (37 pacing studies) NQT was still inducible in 12 cases. During the follow-up period ten patients developed a recurrence of NQT:nine cases out of 12 (75%), in whom NQT was inducible while on antiarrhythmic therapy, and one case out of 25 (4%), in whom NQT was not inducible (P less than 0.001). The sensitivity of TAP in predicting the outcome of the patients with NQT was 90%, and the specificity 89%. The negative predictive value of TAP (prediction of no recurrence of NQT) was 96%, and the positive predictive value (prediction of recurrence of NQT) was 75%. We conclude that TAP is a simple and accurate method for predicting the efficacy of antiarrhythmic treatment in patients with NQT.