The extent and duration of the vibration-induced hyperresponsiveness of arterial smooth muscle to noradrenaline increased as the period of vibratory stimulation became longer. Division of a fixed stimulation time into a few shorter units interposed by intermissions decreased the extent and duration of the hyperresponsiveness. The shorter the length of each unit, the less the hyperresponsiveness. Verapamil effectively suppressed the appearance of the hyperresponsiveness, whereas pretreatment with phentolamine only partially inhibited its appearance. Administration of vitamin E was effective in suppressing the vibration-induced rise of responsiveness to noradrenaline in plasma.