The blood level of soluble IL-6 receptor was measured in patients with different clinical and morphological forms of nonalcoholic fatty liver disease and healthy donors. The relationship of the soluble IL-6 receptor with the content of IL-6, the level of the IL6 gene mRNA, and a number of markers of hepatocyte and peripheral blood leukocyte apoptosis was assessed. It has been established for the first time that progression of nonalcoholic fatty liver disease is associated with changes in the level of soluble IL-6 receptor in the blood. In patients with high activity of nonalcoholic steatohepatitis and liver cirrhosis, the blood concentration of soluble IL-6 receptor sharply decreased in comparison with the earlier stages of progression of nonalcoholic fatty liver disease (liver steatosis, nonalcoholic steatohepatitis of weak and moderate activity). This allows considering the decrease in this indicator as a new diagnostic marker for distinguishing nonalcoholic steatohepatitis of high activity from weak and moderate activity. A close correlation between changes in the level of soluble IL-6 receptor and apoptosis of peripheral blood leukocytes and hepatocytes was revealed.