The goal of the proposed studies is to validate an early marker of Parkinson's disease (PD) that may be able to identify disease onset prior to clinical manifestation. It is now recognized that in PD the onset of brain inflammation and degeneration begins to occur several years prior to neurological symptoms. Our approach uses a glial-specific marker protein, the peripheral benzodiazepine receptor, as an early and sensitive indicator of inflammation and degeneration in the brain. An important feature of this technique is that it can visualize and quantify sites of inflammation and degeneration non-invasively in the living human brain. Early diagnosis of PD would be advantageous in testing therapeutic strategies that could slow the progression of PD.