[A biological approach to the problem of dose fractionation in radiotherapy (author's transl)].

The role of what has come to be called "the four R's" of modern radiobiology is reviewed from a general and applied point of view. Especially, repair of subletal damage, redistribution of cells within their cycle, tissue repopulation, cell reoxygenation, are considered with attention to their intervention in the sterilization of tumor clonogenic cells in human radiotherapy.