Radiation sensitivity of both the brain and spinal cord in prenatal and postnatal stages, in infancy and adult age is represented also in consideration of a combined treatment with methotrexate. In adults, application of important doses of high-energy radiation increases the risk of injurious effects to the central nervous system. If the spinal cord is involved, more than 60% of the radiolesions have a progredient course ending with death. The pathogenesis and disposing factors are referred to, and the incidence of radiation necrosis with regard to age and sex, the degrees of injury and their frequence within different ranges of dosage are analyzed on the basis of data from universal literature. An examination of "tolerance doses" for the spinal cord is made by means of Strandquist-diagrams and of the Ellis-formula. The slopes of regression lines are reported for various "degrees of response" in skin, brain and spinal cord following radiation therapy. In the Strandquist-diagram, slopes of regression lines are dependent on the "degree of response", flattening if skin and spinal cord are affected by radiation in the same degree, necroses having the same slope for both the organs.