We evaluated the patterns of dopamine transporter loss in the striatum of ten controls, twenty patients with Parkinson's disease (PD), and nine with progressive supranuclear palsy (PSP) using (123)I-IPT single photon emission tomography (SPECT). Four ROIs in the striatum correspond to the head of caudate nucleus (ROI 1), a transitional region between head of caudate and putamen (ROI 2), anterior putamen (ROI 3), and posterior putamen (ROI 4). A striatal ratio of specific to nondisplaceable uptake (V3'') was calculated normalizing the activity of the ROIs to that of occipital cortex. V3'' values were significantly reduced in all ROIs of PD and PSP patients, compared with controls (p=0.001). V3'' value in ROI 2 was significantly lower in PSP group, compared with PD group (p=0.02). The percent reductions of striatal uptake in ROI 1, ROI 2, ROI 3 and ROI 4 were 56%, 53%, 64% and 78% in PD patients, whereas 75%, 72%, 75% and 77% in PSP patients, respectively. The reduction patterns of uptake were significantly different between PD and PSP groups (p=0.001). In PD patients, the percent reductions of (123)I-IPT uptake were significantly greater in ROI 3 and 4 compared with ROI 1 or 2, whereas those were similar in all ROIs of PSP patients. In addition, PD patients showed a significantly higher posterior putamen/caudate ratio of reduced (123)I-IPT uptake than the anterior putamen/caudate ratio (p=0.005). Our results implicate that (123)I-IPT SPECT is a relatively simple and reliable technique that may be useful in differentiating PD from PSP.