Objective - to study the influence of multipotent mesenchymal stromal cells (MMSC) transplantation on morphometric parameters of the liver of mature and old laboratory animals with toxic hepatitis. Material and methods. The experiments were performed on mature and old male mice. Toxic hepatitis was caused by intraperitoneal administration of CCl4 at a dose of 50 μg/kg. The cells were transplanted via the tail vein 1 hour after administration of a single dose of carbon tetrachloride. The effect of MMSC on liver morphometric parameters in physiological conditions and after toxic hepatitis development was studied on days 1, 3, 7 after cell transplantation. Results. An increase in mitotic activity, an increase in the number of hepatocytes, hepatocyte nucleus area, and nuclear cytoplasmic index were found in mature laboratory animals with toxic hepatitis on the 3rd day after the introduction of MMSC. At the same time, only an increase in the area of hepatocyte nucleus and nuclear cytoplasmic index was revealed in old laboratory animals. On the 7th day after the introduction of MMSC to the animals with toxic hepatitis, both age groups demonstrated activation of mitotic activity, an increase in the number of hepatocytes, an increase in the area of hepatocyte nucleus and nuclear cytoplasmic index. Conclusions. Changes in liver morphometric parameters in mature and old laboratory animals are realized through mechanisms of both cellular and intracellular regeneration. In addition, the activation of only intracellular regeneration was found in old laboratory animals on the 3rd day after the introduction of MMSC, while in mature laboratory animals there was an increase in cellular and intracellular regeneration of hepatocytes. In later periods in both studied age groups, the change in the main liver morphometric parameters is realized through the activation of both cellular and intracellular regeneration.