OBJECTIVES: In a comparative analysis of the hepatoprotective properties of mediator substances fetal cells were more expression than in essentiale and provided dose-dependent effect.  The aim was to evaluate the effect of mediator substances of fetal cells to hepatocytes during acute liver failure.  METHODS: For this experiment we used an experimental model of chronic hepatitis, where a carbon tetrachloride used as toxic agent, which were introduced into experimental rats at dose of 0,2ml / 100g. The experiment had been lasted 45 days. Thus, the level of alanine aminotransferase at the 2nd day of the experiment in the control group of untreated animals was 4.6 times higher than in intact rats. While the level of aspartate aminotransferase in blood serum of control animals receiving no hepatoprotective therapy increased 1.8 times to 10^thday as compared to intact group. RESULTS: Experimental acute hepatitis accompanied by an increase in the values of thymol 1.5 times already on the 2nd day, on the 5th and 10th days of the experience were even more growth in this indicator when it exceeded the level of the intact group by 3.9 times and amounted to  respectively p<0.05 and p <0.001.  In the control group of animals exposed to the toxic effects of paracetamol and its metabolites to liver cells was observed marked change parameters of cholestasis. Thus, the content of bilirubin in the group of untreated animals on the 2nd and 5th day of the experiment exceeds the index of intact animals by 1.3 times, on the 10th day of the study, it decreased and was 1.2 lower than in the intact group (p<0.001).   CONCLUSIONS: Morphological findings which were found in the experimental groups using the "mediator substances" of fetal cells in a dose of 0.1 ml/kg, showed that their hepatoprotective effect appears to 10th days.