We propose a study to evaluate and develop a new technology to improve movements in patients with Parkinson's disease and to better understand the underlying disease process. Transcranial magnetic stimulation is a painless, non-invasive technique that targets a magnetic field to induce focal pulses of electrical current in the brain. Repetitive trains of transcranial magnetic stimulation have been reported to temporarily improve movements in patients with Parkinson's disease. In transcranial magnetic stimulation, a plastic-encased coil about 9 by 4 inches in size is held next to the head. Repetitive stimulation would be delivered over twenty minutes with patients seated in a reclining chair. A battery of tests will be done before and after both active and sham stimulation to evaluate impact on the movement disorder. These tests include a neurological examination, a walking test, a handwriting analysis, and tests of reaction time, as well as electrophysiological tests. The electrophysiologic tests involve stimulation of the brain with single stimuli delivered over the part of the brain that controls the hands while measuring the electrical activity of muscles with small electrodes taped on the skin. Some of these measures are abnormal in patients with Parkinson's disease and improve with treatments which are known to be effective. We hope to further characterize these electrophysiological signatures of PD both to find out how repetitive transcranial magnetic stimulation might be helpful and to understand the disease process better. Patients who show signs of improvement on the above measurements will undergo repeated stimulation with modification of stimulation parameters in an attempt to enhance beneficial effects.