Dear Friends: The Stanford University Movement Disorder Center and Pallidotomy Program has developed an active research program into the benefits of the surgical procedure known as "Posterior Ventral Pallidotomy". While we have an active clinical program, we are currently recruiting subjects to participate in the research limb. We are seeking patients with medically intractable Parkinson's Disease who have severe on-off periods, L-Dopa induced dyskinesias, are bradykinetic, or have freezing episodes. We will require approximately 1-2 days of your efforts in which you would take a number of paper and pencil tests and motor tasks to serve as control groups for our research program. Participation in this research will in no way jeopardize your ability to receive care, nor future interventions for your disease. If you or your physician have any questions, please don't hesitate to contact Gary Heit, Ph.D., M.D. at (415) 723-5572. If you wish to enroll in this study, please contact Kelly Connell at (415) 725-2585. Thank you for your consideration in this process. We will look forward to hearing from you. Sincerely, Gary Heit, Ph.D., M.D. Gerald D. Silverberg, M.D. Clinical Fellow in Neurosurgery Professor, Neurosurgery