Parkinson's disease (PD) is the debilitating movement disorder, distinguished by dopaminergic and norepinephrinergic neurodegeneration. Apart from candidate gene mutations, several modifier loci have been reported to be associated with the disease manifestation. The Dopamine β-Hydroxylase (DBH) maintains cellular dopamine content and regulates dopamine turn over in neurons. Genetic polymorphisms of DBH are associated with PD and are found to alter plasma DBH activity in patients compared to healthy controls. Therefore, DBH activity in plasma could be a potential and easily detectable biomarkers for alteration of dopaminergic neuronal function in PD.