Spontaneous blinks are occurred by involuntary contractions of m. orbicularis oculi. Although the relationship between Parkinson's disease and a frequency of spontaneous blinks has been an object of study for a long time, the neurophysiological mechanism of spontaneous blinks has not yet been resolved. The aim of this study is to evaluate the generative mechanism of the spontaneous blinks by comparison of both electromyographic (EMG) activities of m. orbicularis oculi and electro-oculogram (EOG) waveforms in the patients with Parkinson's disease and those in the normal subjects. The mean duration of the EMG and the mean amplitude of both the EMG and the EOG in the patients with Parkinson's disease were shorter and smaller than those in the normal subjects by the significant level of 1%, respectively. These results suggested that the function of m. orbicularis oculi for the spontaneous blinks was reduced in patients with Parkinson's disease. The responsible lesion of the Parkinson's disease is degenerative changes of the dopaminergic neurons in the substatia nigra pars compacta. Therefore, the abnormal activity of the basal ganglia which consisted of the substantia nigra pars compacta, the striatum, and the globus pallidus caused hypoactive of the motoneurones of the facial nucleus innervating the orbicularis oculi.