The growing tumor in the organism causes the inflammatory, dystrophic and necrotic changes in the liver and stimulates its regeneration. During X-irradiation there is a summation of the tumor and X-ray effects. The rate of the reparative regeneration is sharply inhibited in later stages of the tumor growth, moreover this inhibition is reduced by irradiation. During X-irradiation poliploidization (the appearance of uninuclear poliploid and increase of binuclear hepatocytes) and sharp proliferation of stroma elements but not proliferation of the parenchyma cells predominate in the mechanism of the liver regeneration.