Electrophysiologic studies are used for diagnosis and treatment in patients with sustained ventricular tachycardia. This method can only be employed if high inducibility of the spontaneous tachycardia can be demonstrated. We therefore investigated prospectively the induction yield in 35 patients with a history of documented sustained ventricular tachycardia. The patients' mean age was 58 years. Coronary artery disease was present in 24 patients, cardiomyopathy in 4, other organic heart diseases in 4, and no heart disease in 3. The ventricular tachycardia induction protocol consisted of three extrastimuli delivered during sinus rhythm and at two pacing cycle lengths, followed by intravenous isoproterenol if no tachycardia was induced before. With the method sustained ventricular tachycardia was induced in 100% of patients with coronary artery disease and cardiomyopathy, in 75% of patients with other heart diseases and in 33% of patients without detectable heart disease. We conclude that electrophysiologic studies have a high yield of sustained ventricular tachycardia induction in patients with underlying organic heart disease. The rational basis for use of electropharmacologic testing therefore exists in these patients. However, in patients without heart disease, the low sensitivity of electrophysiologic studies precludes its use for drug efficacy testing.