Thalamic neurons projecting to the arm area of the motor cortex were identified by their antidromic response to stimulation of that area in two awake monkeys. Neurons were further identified as receiving inputs from the cerebellar nuclei or the internal segment of the globus pallidus by excitatory or inhibitory response to stimulation of these nuclei. Most (33/34) of the thalamic neurons in the cerebello-thalamo-cortical projection and more than half (12/18) of those in the pallido-thalamo-cortical projection changed their firing rate on the lever-lifting hand movement in the reaction-time task. A considerable number of neurons of both groups (14/23 and 3/10) changed their firing rate prior to the onset of the earliest EMG. These findings agree with the model that activities of pallidal as well as cerebellar nuclear neurons related to motor control are transmitted to the motor cortex through the thalamus.