Microinjection into the dorsolateral pontine tegmentum of the muscarinic agonist bethanechol, leading to activation of cholinoceptive pontine reticular formation (pRF) neurons and the related medullary inhi-bitory reticulospinal system, did not modify the threshold, latency and amplitude of the forelimb flexion elicited by unilateral stimulation of the corresponding motor cortex. However, the remaining limbs which displayed a diagonal pattern of postural adjustments showed a dissociation of their postural responses in 2 components: the early component of central origin greatly decreased in amplitude, while the late component attributed to reflex mechanism triggered by the unbalance brought about by the flexion movement increased. Further evidence indicated that the pRF system intervenes in the gain regulation of the early postural responses during the cortically induced limb movement. Stimulation of the motor cortex produces in the cat not only a limb flexion, but also a diagonal pattern of postural adjustments characterized by a decreased force exerted by the limb diagonally opposite to the moving one and an increased force by the other two [6, 7]. The demonstration that the postural adjustments parallel the onset of movement ([8], see also [2, 6]) indicates that they are not of reflex origin, but result from a central command. The lateral vestibular nucleus (LVN), which exerts a direct excitatory influence on ipsilateral limb extensor motoneurons [14], represents a good candidate for such a role [9]. In fact, vestibulospinal (VS) neurons respond to stimulation of the contrala-teral motor cortex [13], an effect which disappears after partial cerebellectomy [11]. Moreover, lesion experiments indicate that the cortical influences responsible for the posturai adjustments during the limb movement utilize the precerebellar lateral reti-cular nucleus and the inferior olive [9, 17].