The authors wanted to evaluate the usefulness of 99Tcm-TRODAT-1 as an imaging agent for measuring changes in dopamine transporter concentrations in Parkinson disease (PD) and correlate the findings to the severity of the disease as measured by the Hoehn and Yahr scale (H/Y). Twenty-two healthy volunteers and 27 patients with PD of H/Y stage I-IV were evaluated. Acquisitions were performed 2 hours after injection of 99Tcm-TRODAT-1. Regions of interest were drawn over the striatum and the cerebellum, and the ratios of striatum-to-cerebellum (ST/CB) were calculated. Patients with PD showed a significant decrease in the striatal uptake of 99Tcm-TRODAT-1 compared to healthy volunteers, and the ST/CB ratios were closely related to the stage of PD. The present study demonstrates that it is possible to visualize and quantify changes in dopamine transporter in the striatum of patients with PD using 99Tcm-TRODAT-1 and SPECT with good correlation to H/Y stage and unified Parkinson's disease rating scale (UPDRS) scale.