Single voxel proton MRS was used to study brain metabolism in the striatum of patients diagnosed with idiopathic Parkinson's disease (PD). Peak metabolite ratios in long echo time spectra were evaluated in 151 patient spectra and 97 age-matched control spectra collected at four participating institutions using identical hardware and clinical protocols. Combining data from all ages (27-83 years old) showed no significant difference between patient and control ratios. However, in an elderly subset of patients (51-70 years old), a significant decrease in striatal N-acetylaspartate (NAA)/choline (Cho) was observed. Also, a significant decrease in the mean NAA/Cho ratio was observed in patients versus controls for patients not being treated with Sinemet (Du Pont Pharm, Wilmington, DE) (hereafter referred to as levodopa/carbidopa). This result is consistent with the hypothesis that NAA may provide a reversible spectroscopic marker for neuronal dysfunction, although a prospective follow-up study will be needed to confirm this. Quantitation of MRS would be useful to exclude the possibility that a change in Cho levels affected the NAA/Cho ratios.