[en] A 10B-dopa analogue, 10B1-para-boronophenylalanine (10B1-BPA) has been found to have a marked melanoma killing effect as expressed by the Do value, 0.9-1.2 X 10(12) n/cm2. The Do value of the neutron alone is 2.8 X 10(12) n/cm2. After the introduction of high LET irradiation into radiotherapy, its higher energy deposition in the target cancer cells is one of the major problems currently to be solved. This can be achieved by our thermal neutron capture therapy in the order of cellular dimensions when we have highly tumor-seeking 10B-compounds available. Our present evidence seems to indicate that our new 10B1-BPA can highly concentrate 10B into melanoma cells, to as much as 11 times the level of the medium in the in vitro system