The aim of the study was to demonstrate the degeneration of the dopaninergic nigrostriatal pathway in Parkinson's disease(PD) and Essential Tremor (ET) by using the cocaine derivative ^99mTc-TRODAT-1 SPECT and correlate the findings to the clinical severities (Hoehn and Yahr scale, H/Y). 28 patients with idiopathic Parkinson's disease, 10 patients with Essential Tremor and 19 healthy volunteers were investigated. The acquisition were performed 3h postinjection of ^99mTc-TRODAT-1, ROIs were drawn over the images of striatum and cerebellum, and ratios of striatum to cerebellar(ST/CB) were calculated. Ratios differed significantly between PD and controls, but ratios didn't show significant difference between ET patients and controls. A significant correlation didn't exist between ratios and clinical severities. Hemiparkinson's patients revealed significantly diminished ^99mTc-TRODAT-1 binding not only clinically affected but unaffected side. Our findings indicated that ^99mTc-TRODAT-1 SPECT is not only a reliable method to discriminate between PD and controls but also a useful tool for differential diagnosis in clinically unclear cases such as ET resembling PD.