In this study, the silent period after transcranial magnetic cortical stimulation was studied in 16 patients with Parkinson’s disease before and after L-Dopa therapy and in 15 normal subjects. In patients and normal subjects the silent period was also studied after peripheral nerve stimulation. The peripheral silent period after supramaximal stimulation of the ulnar nerve at the elbow was obtained during sustained voluntary contraction of the first dorsal interosseus muscle and the cortical silent period after maximal transcranial magnetic stimulation was obtained the same manner. The silent period after transcranial cortical stimulation was shorter in Parkinson’s disease patients than in normal subjects. In patients with Parkinson’s disease L-Dopa prolonged the silent period after transcranial cortical stimulation. The peripheral silent period was similar in normal subjects and in patients and did not change after L-Dopa administration. This findings suggest that while spinal inhibitory mechanisms does not change in Parkinson’s disease, cortical inhibition is decreased. Although, L-Dopa therapy act on these decreased central inhibition.