The work was concerned with the study of 57 gliomas, among which were 30 glioblastomas, 20 astrocytomas, and 7 oligodendrogliomas. Specimens collected from 26 patients who underwent operation for severe craniocerebral trauma, meningioma, and carcinoma metastasis were examined as controls. The proteins of the tumor tissues and those of the brain matter surrounding the tumor and of normal brain matter were fractionated in polyacrylamide gel. It was found that the amount of water soluble protein, both in the total protein content and in all its fractions, was much greater in the glial tumors than in normal brain matter. The effect of 11 factors on the tissue protein composition was studied by factor analysis. The histological structure and extent of vascularization of the tumor as well as the presence of intracranial hypertension were found to produce the highest effect on the fractional distribution of the proteins.