From January 1992 to June 1993, 100 consecutive patients with clinically documented paroxysmal supraventricular tachycardias underwent radiofrequency catheter ablation. Group 1 consisted of 46 patients (male:female = 9:37, age: 46 +/- 13 years) with slow-fast atrioventricular nodal reentrant tachycardia. Radiofrequency current was aimed at the slow pathway area which was identified by both anatomical and electrophysiological methods. A mean application of 8 +/- 9 was delivered at a mean power of 22 +/- 4 watts with a mean duration of 21 +/- 3 seconds. Selective ablation of slow pathway conduction was achieved in 28 patients and modification of slow pathway conduction in 12 patients. Antegrade fast pathway conduction was ablated in 3 patients, and retrograde fast pathway conduction in 1. Mean peak CPK was 156 +/- 117 IU/L after ablation. Neither AV block nor clinical recurrence was found during 9.7 +/- 5.1 months follow up. Group 2 consisted of 54 patients with accessory pathway (AP) mediated atrioventricular reciprocating tachycardia. For 35 patients (M:F = 21:14, age: 40 +/- 12 years) who had left-sided accessory pathway, catheter ablation was approached by the retrograde trans-aortic technique in 33 patients and by the transseptal left atrial approach through patent foramen ovale in 2 patients. The mean energy delivered was 28 +/- 5 watts for a duration of 27 +/- 12 sec and 9 +/- 8 applications. The accessory pathway conduction was successfully ablated in 30 patients (86%). Mean peak CPK was 392 +/- 534 IU/L. Cardiac tamponade occurred in 1 patient and transient cerebral ischemia in another, but without mortality. No clinical recurrence was found during 9 +/- 4 months follow-up. Nineteen patients (M:F = 7:12, age: 36 +/- 11 years) had right-sided AP. The mean energy required for successful ablation was 30 +/- 4 watts for a duration of 35 +/- 15 sec and 12 +/- 9 applications. Mean peak CPK was 147 +/- 70 IU/L. Clinical recurrence occurred in 3 patients (15.8%), 1 of them had subsequent successive ablation. The overall immediate procedure success rate for right-sided AP was 65%. In conclusion, radiofrequency catheter ablation is a safe and effective treatment modality for patients with paroxysmal supraventricular tachycardias.