Total body irradiation produces a sufficient immunosuppression to prevent an allograft rejection. It can be used with chemotherapy as an "intensive" treatment aiming at the complete eradication of a malignancy--with the resulting bone marrow aplasia needing an autologous or allogeneic transplantation. In either case, a dose of some 10 Gy has to be delivered in the whole body, in one session at low dose rate or fractionated between several sessions. Such a dose is usually well tolerated--at any rate it does not carry too high a risk to contribute to induce an interstitial pneumonitis or a venous occlusive disease of the liver. The antitumoral efficacy of such limited dose is mainly important against very radiosensitive tumours--first of all leukemias and lymphomas. Yet some groups use also total body irradiation in the treatment of some solid tumours of dismal prognosis--for instance in case of advanced neuroblastomas or Ewing's sarcomas.