[en] With respect to anti-tumor effect of radiation, antigenicity and involvement of immunity of an individual with cancer were evaluated under both conditions of natural and insufficient immunity. In animal experiments, it is clear that immunity of the host, especially the function of T-cells, has much to do with the curability of cancer by radiotherapy. In some type of human cancer, not only the histological findings in its healing process following x-ray irradiation but a number of clinical and in vitro experimental results strongly suggest the presence of antigenicity of the T-cells, although it is quite little. The experiments made in a combination of human cancer and nude mice showed a possibility of non-T cells being involved in this mechanism irrespective of whether it is specific, non-specific or not having such an important role as T-cells. There are many problems left unsolved. However, radiotherapy of cancer should be undertaken by maintaining or further improving the immunity of the body in order to obtain good results. (Ueda, J.)