Electrophysiologic testing is warranted in patients with the Wolff-Parkinson-White (WPW) syndrome presenting with rapid atrial fibrillation (AF) or ventricular fibrillation. Indications are less clear in patients presenting only with atrioventricular reentrant tachycardia (ART). A knowledge of propensity of this latter group to show a rapid ventricular response in the event of AF and the ability of electrophysiologic testing to reproduce the type and rate of clinical arrhythmias are relevant to this decision. The records of 126 symptomatic patients with manifest WPW syndrome were reviewed and separated into 4 groups according to presentation: group 1--AF; group 2--ART; group 3--palpitations suggesting ART; and group 4--AF and ART. All patients except those in group 3 had electrocardiographically documented clinical arrhythmias, and these arrhythmias were compared with those induced during electrophysiologic testing. The shortest RR interval during induced AF and the cycle length of induced ART correlated well with those occurring clinically (r = 0.72, p less than 0.00001), as did the cycle length of induced ART (r = 0.79, p less than 0.00001). Patients presenting with AF (65%) had a higher incidence of atrial vulnerability (48%) and sustained AF at electrophysiologic testing than those presenting with ART (16% and 5%) or undocumented palpitations (27% and 21%). Forty-one percent of patients with ART and 51% with undocumented palpitations had potentially lethal rates (shortest RR interval less than 250 ms) during induced AF. The ability to reproduce clinical arrhythmias and the frequency of rapid rates during AF induced in patients presenting with only ART or undocumented palpitations supports the recommendation for electrophysiologic testing in symptomatic patients with WPW.