The antidromic activation of facial nucleus motoneurons to the stimulation of various branches of the facial nerve was studied by means of intracellular recording in cats. The time and amplitude characteristics of separate components of the antidromic spike were analyzed and fast and slow after-potentials were distinguished. A correlation was shown between the duration of the falling phase of the SD spike, the duration of its after-hyperpolarization and the impulse conductance time in the axon. Data indicating the absence of the recurrent collateral pathway in the facial nucleus motoneurons were obtained. The possible functional significance of the after-potentials is discussed.