Inclusion Criteria: - Subjects must have a diagnosis of bilateral, idiopathic Parkinson's Disease who have been enrolled and treated with intraputaminal infusion of liatermin in a previous Amgen/Medtronic-sponsored trial (protocols 20010109 or 20030160) or the Bristol open-label study - At time of implant (Study 20030168), subjects need to have been 35 to 70 years of age