The use of low level electrical stimulation when applied over the head, also called transcranial direct current stimulation (tDCS), is being tested by several groups of researchers to see if tDCS can improve movements of persons with damage to the brain. The safety and potential benefits of tDCS to children or adults patients who are paralyzed because of brain damage are reported in the medical literature. In addition, some patients with Parkinson's disease (PD) experience improvement in memory and report better use of the hand after tDCS. The treatment requires putting electrodes (pads) over the head and sending very small amount of electrical current that the patient may feel as "little tingling". Application of tDCS takes 20 min. In this study we wish to test if tDCS application can improve stepping and walking ability of subjects with PD and if the improvement is the same as when walking on treadmill. We plan to test the subject's ability to step when pulled by a laboratory testing system and also test his/her walking ability. There will be 3 sessions 7 days apart. In the first session the subject will be tested then treated for 20 min with tDCS and then tested again. In the second session the subject will be tested then walk on a treadmill for 20 min then tested again. In the third session the subject will be tested then walk on the treadmill for 20 min while receiving also tDCS and tested one last time at the end of the session. Each session will take between 2 and 3 hours.