The nuclear periphery of 10 glioblastomas multiforme, 5 astrocytomas, 2 ependymomas, 2 medulloblastomas, and 3 meningiomas, were examined with the electron micro-scope. All tumors exhibited the marginal heterochromatin granules forming a dense beaded row and running parallel to the inner nuclear membrane. The marginal heterochromatin granules in all tumors were sometimes not in contact with the inner nuclear membrane, and seemed to be separated from the inner nuclear membrane by a moderately dense layer, about 70 Å thick. The inner side of this layer was irregular in contour, because of the presence of the spherical heterochromatin granules. In certain glioblastoma multiforme and astrocytoma as well as fibroblastic meningioma, the fibrous lamina or the nuclear limiting zone was obviously found between the inner nuclear membrane and the marginal heterochromatin granules. It was similar in density as the nucleoplasm in the glioblastoma multiforme as well as the astrocytoma and homogeneously dense in the fibroblastic meningioma. The inner side of this nuclear peripheral zone exhibited some indentation, because of the protrusion of the marginal heterochromatin granules into the nuclear limiting zone, and did not possess its own delimiting membrane to keep the nuclear chromatin separated from the substance of the nuclear limiting zone. The fibrous lamina or the nuclear limiting zone in the fibroblastic meningioma appeared interrupted or greatly attenuated and poorly defined on the inner side of the nuclear pore, and often seemed to continue unchanged across the nuclear pore. In the E.M. examination of brain tumors, there was a variation in thickness and appearance of the nuclear limiting zone within the same type of cells, and the nuclear limiting zone was often absent.