The authors have studied the histological, histochemical, and ultrastructural aspects of eight corticectomies of epileptogenic foci in the medial surfaces of frontal lobes. In all cases they were able to see more gliosis and fewer neurons than normal. The shape and number of dendritic spines were thought to be normal with the Golgi-Cox method. The histochemical study showed an increment of activity of Glucose-6-Phosphatase, Glucose-6-Phosphatedehydrogenase, adenosintriphosphatase, and acid phosphatase. The electron microscope showed, in every case, a variety of changes, among which the authors can point to perivascular lipid accumulation, and an increase of lipofuscin bodies in the cytoplasm of pyramidal cells.