[en] Repopulation is known as one of the principal phenomena involved in fractionated radiotherapy. Experimental results obtained in the laboratory and in literature on the repopulation were presented. These data indicate that tumor cells immediately after irradiation exhibit rapid proliferation which is followed by a reduced growth rate. Alterations in the volume doubling time and in the cell cycle time were involved in these phenomena. There has been another report in the literature of rapid repopulation after irradiation in human tumor radiotherapy. (Evans, G.)