As indicated by the title, it is the object of this paper to give insight into some of the tasks which are to be taken up in radiobiological research at a radio-therapeutic cancer center. Since problems and not results are to be discussed, the lecture should only throw light on a field previously unheeded and on some of the means by which it may be attacked. Neither chemotherapy nor internal radiotherapy (with radioisotopes) has proved of such effect in cancer treatment as to justify the disregard of any possibility of pushing the rational utilization of classical x-ray and radium therapy a step further. In the present state of radiotherapy, involving large total doses which must pass through considerable volumes of tissue, the necessity of paying due regard to the stress on the irradiated organism should be more evident than before. Outstanding examples are Coutard therapy of tumors in the upper parts of the respiratory and digestive tracts, rotation treatment of cancer of the esophagus, and radium and x...