Proton MR spectroscopy (1H-MRS) has been previously performed in Parkinson's disease (PD) and parkinsonian syndromes to evaluate in vivo concentrations of basal ganglia and cerebral cortex metabolites such as N-acetylaspartate (NAA), choline (Cho), and creatine (Cr). However, this technique has never been used to evaluate motor cortex in untreated PD patients. In this study, single-voxel 1H-MRS of basal ganglia and motor cortex was carried out in 10 de novo patients with PD and 10 age-matched healthy controls. A significant reduction in the NAA/Cr ratio was observed in the motor cortex of PD patients compared with controls (p)<(0.01). Basal ganglia spectra did not allow any evaluation due to the presence of artefacts related to inorganic paramagnetic substances. The motor cortex reduction of the NAA/Cr ratio in de novo PD patients may reflect an altered neuronal functioning due to a loss of thalamocortical excitatory inputs and may represent an in vivo marker for the diagnosis of PD.