A 44-year old male with Wolff-Parkinson-White syndrome presented with atrial fibrillation. The patient was found at the electrophysiological study to have two accessory pathways, one concealed and the other conducting exclusively in the anterograde direction. After radiofrequency catheter ablation of the anterograde conducting pathway, orthodromic reciprocating tachycardia, which previously could not be induced despite an aggressive protocol, was easily induced. Ablation of the concealed pathway resulted in termination of the tachycardia and suppression of inducibility. We propose that interaction between the two accessory pathways resulted in an inability to induce reciprocating tachycardia.