The results of the examination of the muscle tone by passive movement of the extremity at a low and high rate in patients with spasticity are discussed. In parkinsonism high resistance was noted to passive movements of the extremity at a low rate (with a period of oscillatory movement of 100 s and more) as well as in the first cycles of rapid sinusoidal movement (with a period of 1 s) if the extremity had been at rest for a lengthy period of time. In spasticity of other etiology, there was a gradual increase of the amplitude on the mechanomyogram in high rates of passive movements, which was evidently due to growth of stimulation in the stretch-reflex arc from cycle to cycle as the result of sumation with trace stimulation from the preceding cycles. The shape of the spectromechanomyogram, which is marked by a rise in the region of the high rates, is considered to be a sign of spasticity, whereas the size of this rise is accepted as a quantitative index of the spastic component of the muscle tone.