Right ventricular outflow tachycardia is a distinct subgroup of idiopathic ventricular tachycardia (VT) with characteristic clinical and electrophysiologic properties. This study was planned to evaluate the effects of adenosine on idiopathic right ventricular tachycardia in children, and to assess the long-term efficacy of verapamil treatment. Diagnostic tests including electrocardiogram, chest roentgenogram, echocardiogram, exercise stress test and 24-hour ambulatory electrocardiographic monitoring were performed in each patient. Adenosine was administered in increasing amounts until an effective dose or a maximal dose of 300 micrograms/kg was reached. In adenosine-sensitive patients verapamil was given orally (3-10 mg/kg/day) for long-term suppression of arrhythmia. Seven patients with a mean age of 10.2 +/- 4.7 years were enrolled in the study. There were five male and two female patients. Six patients had VT, and one patient had frequent ventricular ectopic bests. Arrhythmia originated from the right ventricle in all patients. Adenosine was effective in terminating the arrhythmia in all patients, with a mean effective dose of 183 +/- 75 micrograms/kg. Favorable long-term results (mean follow-up period 17 +/- 8 months) were obtained with verapamil treatment at an average dose of 6.3 +/- 2.2 mg/kg. In conclusion, adenosine can be used effectively for termination of VT originating from the right ventricular outflow tract in children. In these patients verapamil may be considered as the drug of choice for long-term therapy.