The determinants of long-term clinical outcome were studied in 42 patients with recurrent ventricular tachycardia (VT) or ventricular fibrillation (VF) who were treated with amiodarone as the sole antiarrhythmic agent. Of the 42 patients, 11 (26%) either died suddenly or had recurrent, symptomatic, sustained VT during a mean follow-up period of 10 months (range 0.3 to 45). Of the 19 patients without inducible VT/VF during electrophysiologic study while receiving amiodarone, 1 patient died suddenly but no patient had recurrent VT/VF. Ten of the 23 patients (43%) with persistently inducible arrhythmia have died suddenly or have had recurrent VT/VF. Using survival and stepwise logistic regression analyses, 2 significant independent predictors of recurrent arrhythmia were identified; persistently inducible VT during electrophysiologic testing in patients receiving amiodarone therapy (p less than 0.002) and the left ventricular ejection fraction at rest (p less than 0.05). The predictive accuracy of the response to serial electrophysiologic testing during amiodarone therapy was 67%, the sensitivity was 58% and the specificity was 91%. Thus, serial electrophysiologic testing is useful for determining the prognosis in patients with inducible VT/VF treated with amiodarone.