Neural and psychologic factors have been implicated as risk factors for ventricular arrhythmias and sudden death in man. However, the relation between these factors and arrhythmia has hitherto not been systematically explored. We examined the effect of psychologic stress testing in 19 patients with advanced grades of ventricular arrhythmias. Psychologic stress consisted of mental arithmetic, reading from colored cards and recounting emotionally charged experiences. Such testing induced a significant increase in ventricular premature beat frequency in 11 of 19 patients (P less than 0.05). One patient experienced paroxysms of ventricular tachycardia. In 14 of these 19 patients elicitation of vagal or sympathetic autonomic reflexes failed to induce significant arrhythmia in all but one patient. It is concluded that (1) objective psychologic tests may precipitate ventricular arrhythmia in susceptible patients, and (2) evocation of peripheral autonomic reflexes is an insufficient trigger for enhanced ventricular ectopic activity.