Phosphorus magnetic resonance (MR) spectroscopy allows noninvasive measurement of phosphate-containing compounds and pH within brain cells. The authors obtained localized phosphorus MR spectra from 10 normal brains, four low-grade astrocytomas, six glioblastomas, four meningiomas, and three pituitary adenomas and found differences in the spectra of each tumor type. Compared to normal brain, the spectra from low-grade astrocytomas showed a significant reduction of the phosphodiester (PDE) peak. Glioblastomas were characterized by a significant reduction of the PDE peak, elevation of the phosphomonoester (PME) peak, and a relatively alkaline intracellular pH. The spectra from meningiomas and pituitary adenomas were markedly different from the glial tumors. Meningiomas showed significant reductions in phosphocreatine, PDE, and inorganic phosphate, as well as a relatively alkaline pH. Pituitary adenomas resembled meningiomas, but had a much higher PME peak. Although the number of tumors studied was small, there appears to be a characteristic spectrum associated with these different tumor types. The present findings can be useful in the preoperative identification of these tumors and in furthering understanding of their growth and metabolism in vivo.