Phosphorylethanolamine (PEA) is the major component of the phosphomonoester peak detected by phosphorus-31 magnetic resonance spectroscopy, but the absolute concentration has not been determined. This study measured the PEA concentration in biopsy specimens of brain tumors and lobectomized cerebral cortex using high-performance liquid chromatography. The concentration of PEA was 118.5 ± 10.0 μmol/100 g wet wt in cortex, and was significantly higher in malignant gliomas, metastatic pulmonary adenocarcinoma, and neurinoma. The concentration of PEA was especially high in pituitary adenoma, malignant lymphoma, and medulloblastoma.