Electrophysiological studies with extracellular microelectrodes demonstrate that, in anesthetized cats, high-frequency stimulation of the cerebellar nuclei could cause an increase or a decrease in spike activity recorded from neurons of the ipsilateral and contralateral motor cortex. Some of these neurons were also responsive to antidromic stimulation. This suggests that the cerebellum can exert and influence not only on the cortical interneurons but also on neurons directly concerned with motor function. In unanesthetized animals, responses of neurons in the ipsilateral and contralateral motor cortex could be evoked by a single stimuli applied to the cerebellar nuclei. No change was produced by ablation of the contralateral motor cortex. Thus, the possibility of transcallosal transmission was eliminated. The absence of any evoked response to single stimulus in animals under barbiturate anesthesia indicates that, aside from the well-known cerebellothalamocortical pathway, there are other cerebellocortical pathways which are resistant to barbiturate action and which probably involve the reticular formation of the midbrain and other basal structures of the cerebrum.