Despite the many advances made in the diagnosis and therapy of cancer, the mortality rate is still about half that of the incidence rate. However, the odds are not evenly distributed. Prognosis for some cancers is good, but for others, few patients will survive 12 months. This latter group of cancers is characterised by a proclivity to disseminate malignant cells in the host organ. The degree of surgery possible may be limited by the critical nature of the organ, and chemotherapy and radiotherapy are of palliative value only. In some cases systemic metastases occur, but in other cases, failure to achieve local control results in death. First among these cancers are the high grade brain tumours, astrocytoma 3,4 and glioblastoma multiforme. Local control of these tumours should lead to cure. Other cancers melanoma metastatic to the brain, for which a useful palliative therapy is not yet available, and pancreatic cancer for which localised control at an early stage could bring about improved prognosis. Patients with these cancers have little grounds for hope. Our primary objective is to reverse this situation with Neutron Capture Therapy (NCT). The purpose of this fourth symposium is to hasten the day whereby patients with these cancers can reasonably hope for substantial remissions. The first symposium on NCT was held in Boston in 1983, followed by Tokyo in 1985 and Bremen, Germany in 1988.