Screening and baseline evaluation - Participants are evaluated with a medical history, physical examination and neurologic evaluation, blood tests, urinalysis, electrocardiogram (EKG), 24-hour holter monitor (heart monitoring), and cardiology consultation. A chest x-ray and MRI or CT scan of the brain are done if needed. If possible, patients stop taking all antiparkinsonian medications except levodopa (Sinemet) for one month (2 months if taking Selegiline) before the study begins and throughout its duration. (If necessary, patients may use short-acting agents, such as Mirapex, Requip or Amantadine.)