The high-grade malignant gliomas (anaplastic astrocytomas and glioblastoma) have a very bad prognosis since the available methods of treatment (surgery, radiotherapy and chemotherapy) are unable to control the progression of the disease for long. The use of specific monoclonal antibodies labelled with a suitable isotope (iodine-131 or yttrium-90) represents an effective approach to hamper tumour regrowth. Some authors have injected the antibodies intravenously, or have tried to increase the tumour/background ratio with the avidin/biotin system. In many cases the labelled monoclonal antibodies were injected directly into the tumoral bed after the operation. The authors' experiences concern a quite large locoregional radioimmunotherapy study which was performed by using antitenascin antibodies labelled initially with 131I and more recently with 90Y. The clinical results demonstrate the ability of this technique to control, for a long time, the growth of these tumours. The glioblastoma median survival was prolonged to 25 months (131I group) or 31 months (90Y group). The response rate (which comprises PR, CR and NED) was 47.1% (glioblastoma 131I group) or 40% ( glioblastoma 90Y group). In many cases a significant tumour shrinking effect was radiologically demonstrated. The use of 90Y proved more favourable in bulky lesions, and reduced the radioprotection problems.