PURPOSE: To determine whether 1H magnetic resonance spectroscopy (MRS) is useful in differentiating idiopathic Parkinson's disease (IPD) from progressive supranuclear palsy (PSP), based on metabolite ratios. MATERIALS AND METHODS: Using a 1.5 T MR Unit, single voxel 1H MRS using STEAM with a TR of 2000ms and a TE of 135ms was performed in seven PD and eight PSP patients. Five age-matched volunteers(mean age, 63 years) andanother five younger healthy volunteers(mean age, 30 years) were studied as normal controls. The regions of interest were the putamen and pallidum, with a size of 2 X 2 X 2cm. After measuring the spectral intensities ofeach metabolite (N-acetylaspartate=NAA, choline=Cho, creatine=Cr and lactate), relative peak height ratios ofNAA/Cr, Cho/Cr and Naa/Cho, and lactate levels among four groups were compared. RESULTS: NAA/Cho and NAA/Crratios were statistically lower in the PSP group than the IPD group (1.21 ±0.26 versus 1.45 ±0.20, and 1.26 ±.23 versus 1.38 ±0.19, respectively : p<0.05). NAA/Cho and NAA/Cr ratios were significantly lower inage-matched controls than in younger normal controls (1.39 ±0.21 versus 1.76 ±0.15, and 1.36 ±0.13 versus1.79 ±0.17, respectively : p<0.05). However, NAA/Cho and NAA/Cr ratios between age-matched controls and IPD werenot significantly different (p>0.05). Cho/Cr ratios were not different among four groups. Lactate was not detectedin any patients. CONCLUSION: NAA/Cho and NAA/Cr ratios in the corpus striatum were significantly lower in the PSP group than in the age-matched control and IPD groups. These results suggest that loss of neuron cells in thecorpus striatum is more prominent in PSP than in IPD, and that NAA/Cho and NAA/Cr ratios may help in differential diagnosis of IPD and PSP.