Following injection of horseradish peroxidase (HRP) solution into the rat and monkey temporalis muscle, a similar pattern of nuclear representation was found in the motor trigeminal nucleus. Labelled neurons were seen throughout the rostro-caudal extent of the ipsilateral motor trigeminal nucleus, in its dorsal, intermediate and ventral portions and its dorsomedial, ventromedial and ventrolateral corners. In addition to the motor trigeminal nucleus labelled neurons were also found in the ipsilateral trigeminal ganglion and mesencephalic trigeminal nucleus. The results were discussed.