Studies were performed in 20 patients with symptomatic ventricular tachycardia (VT) to determine the efficacy of bethanidine compared with procainamide in preventing VT induced by programmed electrical stimulation. Before administering bethanidine, 5 to 10 mg/kg, the patients received 15 mg of protriptyline orally 24 and 2 hours before electrophysiologic studies to prevent the orthostatic hypotensive effects of bethanidine. Sustained VT (VT not spontaneously stopping) was induced in 8 and nonsustained VT (10 beats or more, terminating spontaneously) was induced in 4 patients. Bethanidine, 5 mg/kg, protected in 7 patients, and 10 mg/kg protected 1 additional patient. Procainamide, 1,000 and 1,500 mg intravenously, protected 8 of 16 patients. Bethanidine prevented VT induction in 50% of the patients not protected by procainamide. Bethanidine facilitated VT induction in 3 patients, while procainamide facilitated VT induction in 1 patient. Four patients with symptomatic VT have received bethanidine therapy for an average of 11 +/- 1.3 months, without clinical recurrence of their VT. Concomitant administration of protriptyline attenuated the acute hemodynamic changes caused by bethanidine and chronic combined therapy of protriptyline and bethanidine abolished the severe orthostatic changes in blood pressure caused by bethanidine. These studies show that bethanidine is effective in preventing VT induction and, thus, its use may not be restricted only to cases of primary ventricular fibrillation.