Selective section of trigeminal sensory and motor nerves was carried out in two experiments designed to examine the contribution of this sensorimotor system to the control of instrumental responses reinforced with food or water. Unilateral section of either V sensory or V motor nerves had no significant effect on lever pressing. Bilateral section significantly reduced lever pressing, and the deficit was greatest in subjects with trigeminal motor nerve section. Thus trigeminal orosensory or oromotor denervation disrupts performance on a food- or water-reinforced task whose execution does not require a trigeminally mediated response. The results are discussed in terms of motivational and reinforcement accounts of instrumental learning.