[en] The effects of X irradiation (2.9 and 5.8 Gy directly before 2/3 hepatectomy) upon the course of rat liver regeneration were followed for 21 days after partial hepatectomy. The course of regeneration was evaluated on the basis of ³H-thymidine incorporation, DNA content in the hepatocyte nuclei, mitotic activity, frequency of the binucleate hepatocytes, concentration of the nuclei in the tissue and their total number in the organ, furthermore, the DNA content of the organ and its weight. The X-ray induced damage of the liver was manifested in the course of regeneration by the changes of all followed parameters the extent of which depended on the dose of irradiation. First changes were found already 18 hours after partial hepatectomy. The most remarkable differences against the non-irradiated controls were the inhibition of the first proliferation wave and the retarded increase in the number of nuclei in the organ. An attempt was made to quantify the changes of the parameters during the regeneration of the liver after irradiation. (author)