Electrophysiological properties of the interpositus-rubral transmission were studied in anaesthetized cats. The axons of interpositus neurones were stimulated either at their origin in the interpositus nucleus or at their terminal in the ventrolateral nucleus of the thalamus. Impulses of the interpositus axons produced in the red nucleus neurones excitatory postsynaptic potentials (EPSPs) monosynaptically. As a unique feature, these EPSPs exhibited very little facilitation or depression during double shock or tetanic stimulation. Correspondingly, the unitary EPSPs evoked by the threshold stimulation showed little failure during many successive trials. The number of the interpositus axons converging onto a single red nucleus cell was about 50, when calculated from the ratio of the maximum rising slopes between the unitary and maximal EPSPs evoked from the interpositus nucleus.