The aim of this study was to evaluate the efficacy of (31)P magnetic resonance spectroscopy ((31)P-MRS) in the differentiation and staging of brain tumors. Fifteen volunteers and 44 patients with brain tumors (14 meningiomas, 13 low- and 17 high-grade gliomas) were prospectively evaluated by (31)P-MRS. The pH (r=0.493, p<0.001), [Mg(+2)] (r=0.850, p<0.001) PME/α-ATP (r=0.776, p<0.001), PDE/α-ATP (r=-0.569, p<0.001) and (PCr+β-ATP)/Pi ratios were well correlated with tumor differentiation. High-grade gliomas had significantly higher pH (r=0.912, p<0.001) and [Mg(+2)] (r=0.855, p<0.001) and PME/α-ATP (r=0.894, p<0.001) ratio, and lower PCr/α-ATP (r=-0.959, p<0.001), Pi/α-ATP (r=-0.788, p<0.001) and PDE/α-ATP ratios (r=-0.968, p<0.001) than those of low-grade gliomas. Changes in (31)P-MRS parameters by the degree of malignancy are good indicators of increased anaerobic metabolism and hypoxia of tumoral tissue to compensate intratumoral energy deficiency. (31)P-MRS parameters are very useful for grading and differentiation of brain tumors.