This is an application for a Parkinson's Disease Clinical Center (PDCC) at the University of Michigan. The goals of this PDCC are identification of subjects with early, mild Parkinson's disease (PD), their recruitment into pilot and large, multi-arm trials of neuroprotective treatments, follow up of recruited subjects until trial completion, and post-trial follow up of subjects to ascertain the presence of treatment effects. Subjects will be recruited from the existing referral base of clinics at the University of Michigan, the Ann Arbor Veterans Affairs Medical Center, via state-wide publicity of the trial to neurologists in Michigan, and through the major lay PD organization in Michigan, the Michigan Parkinson's Foundation (MPF). We are already working with the MPF on statewide educational and clinical care activities for PD. The established collaborations and state-wide range of activities will enhance recruitment of appropriate subjects within Michigan. Subjects will be enrolled and followed by experienced Movement Disorder clinicians with prior significant experience in clinical trials. Our center has developed a promising objective marker of disease progression; [14C]dihydrotetrabenazine positron emission tomography (DTBZ-PET). A subset of subjects recruited at our site and surrounding sites could be followed serially with DTBZ-PET. In pilot trials, this subset could be used to evaluate DTBZ-PET as a biomarker of disease status and possibly as a screening method for evaluation of putative neuroprotective agents. In large, multi-arm trials, a subset of patients would be followed with DTBZ-PET as an objective marker of disease progression. The use of DTBZ-PET will be enhanced by sharing of subjects from other PDCCs within Michigan to ensure efficient use of PET imaging.