Participants will be evaluated with a medical history, physical examination, detailed neurologic evaluation, routine blood tests, urinalysis and an electrocardiogram. They will also have a 24-hour holter monitor (heart monitoring) and cardiology consultation. A chest X-ray and MRI or CT scan of the brain will be done if needed. Patients will, if possible, stop taking all antiparkinsonian medications except levodopa (Sinemet) for one month before the study begins and throughout its duration. (If necessary, patients may use short-acting dopamine agonists, such as Mirapex and Requip.)