The Authors refer about the treatment of neoplastic tissues (osteosarcomas) by microwave hyperthermia associated with radiation therapy. They used a diathermy device working at 27 MHz, and a linear accelerator at 5.7 MeV. They studied histologically the degree of necrosis, and saw that necrosis is obtained also by smaller amount of rads than habitual, but necrosis was not diffuse uniformly: just some zone were vital. The Authors suggest indications of the method, and remark the technical problems of the same.