The stretch and unloading reflexes were studied on extensor muscles of the hindlimb of decerebrated cats. It had been shown that nonlinear properties of the muscle dynamics were transformed under the reflex control and hysteresis inherent in the muscle itself was not removed by the stretch reflex. Hysteresis of the stretch reflex led to uncertainty of the equilibrium value of the muscle length and the equilibrium length depended on the movement prehistory. Stiffness of the muscle lengthening was shown to depend on the point of change in the movement direction. The observed nonlinearity of the stretch reflex was discussed from the functional point of view.