It is well established that motor experience induces structural and functional plasticity within the central nervous system. It is less well investigated whether reduced motor activity in relation to immobilization is also associated with plastic neuronal changes. The present experiment examined the effect of 1 week of immobilization on transmission in the corticospinal pathway and the central part of the monosynaptic stretch reflex. In ten healthy volunteers the nondominant forearm, hand and fingers were immobilized by a cast for one week. EMG was obtained from m. Flexor Carpi Radialis (FCR) and m. Abductor Pollicis Brevis (APB). Motor evoked potentials (MEPS) elicited by transcranial magnetic stimulation and H-reflexes were obtained at rest and during tonic contraction (10% of MVC) in both muscles. Maximal voluntary flexion torque decreased significantly following immobilization without any changes in the flexion torque elicited by supramaximal stimulation of the median nerve. Both at rest and during tonic contraction the H-reflex increased significantly following immobilization without significant changes in Mmax. MEP amplitudes did not change significantly following immobilization. One week after cast removal all measurements had returned to preimmobilization levels. These results show that immobilization of only one week duration is associated with reversible adaptive changes in the gain of the central part of the monosynaptic stretch reflex.