This is a report of a case of stable uninterrupted spontaneous ventricular tachycardia which could be temporarily terminated by a strong increase in vagal tone reflexly induced by phenylephrine, 0.2 mg I.V. Following its abolition with procaine amide, 100 mg I.V., ventricular tachycardia was found to be reinducible by deep inspiration for limited periods of time which varied directly with the magnitude of the inspiratory volume. This effect was enhanced by vagal inhibition (atropine, 0.6 mg I.V.) and attenuated or prevented by vagal stimulation (carotid sinus massage or edrophonium 10 mg I.V.). It was concluded that a deep inspiration can, under some circumstances, induce ventricular tachycardia by a mechanism of vagal withdrawal.