Effects of in vitro and in vivo vibratory stimulations were studied on dose-response relationships of noradrenaline in excised femoral arteries of dogs and rats. The responsiveness of these arteries were enhanced after the application of the stimulation. The degree of the hyperresponsiveness was dependent upon frequency, amplitude, and duration of the stimulation. Based on the experimental results, a possible explanation was offered for Raynaud's phenomenon in vibration disease.