Swimming training of rats led to a change of functional condition of hepatocytes accompanied by the changes in nuclei distribution by classes of DNA ploidity. The blood sugar level and glycogen content in the liver of trained rats were much greater than in the untrained animals 20 and 48 hours after partial hepatectomy. Reparative regeneration following partial hepatectomy in trained rats was characterized by a peculiar distribution of nuclei by classes of DNA ploidity and by entrance into the synthesis of diploid nuclei only, 20 hours after the operation.