We evaluated the effects of amiodarone in 45 patients with recurrent ventricular tachycardia or ventricular fibrillation. At a mean follow-up time of 12.7 +/- 8.8 months (range, three to 36), amiodarone was successful in nine of 16 patients with recurrent ventricular fibrillation and 21 of 29 with recurrent ventricular tachycardia. During amiodarone therapy, ventricular tachycardia could be induced in 18 of 19 patients in whom it had been induced before therapy, but only six of these 19 had spontaneous recurrence during follow-up. Side effects included corneal microdeposits, hyperthyroidism, blue skin, nausea, and symptomatic bradycardia. Pulmonary fibrosis occurred in three patients. Doses of up to 2000 mg a day did not produce cardiac toxicity, but neurologic side effects precluded long-term therapy at this dose. We conclude that amiodarone is effective for long-term therapy of recurrent ventricular tachyarrhythmias, that induction of arrhythmia during therapy does not always predict efficacy, and that side effects are frequent but do not usually limit therapy.