[en] The late damage of the brain and spinal cord, due to consecutive intensive treatments with chemotherapy and total body fractionated irradiation, in leukemic patients is discussed. Data indicate that such damage depends more strongly on the number of fractions and to lesser extent on the overall time of treatment than damage to other tissues. Without presupposing a specific mechanism of action, empirically developed formulae have been derived in order to enable a comparison of total doses administered in a given fractionated scheme with other total doses and modes of application. In spite of various uncertainties which are considered, it appears that the risk of CNS damage might not be negligible and that exact knowledge of preceding treatments as well as careful dosimetry and observation are required to evaluate risks as early as possible. (U.K.)