The results of study of toxicity of the newly created «Injectable Mevesel» during acute and chronic experiments are presented. There were no lethal cases at intragastric and intramuscular injections, only short-time inhibition of laboratory animals receiving the drug at a dose of 10.0 ml was observed. There were no lethal cases of test animals during the experiment in the conditions of study of accumulation properties of «Injectable Mevesel». Total average dose of the drug administered made up 162500 mg/kg, and accumulation coefficient was respectively 5.3. In the study of morphological blood parameters of rats after intramuscular injection of «Injectable Mevesel» in increasing doses, probable increase in neutrophils count by 36.1%, and probable reduction in lymphocytes count by 15.2% were found. Administration of the drug in increasing doses significantly affects the functional state of internal organs of experimental animals (liver) and causes significant degradation of the membranes of hepatocytes, as evidenced by increased activity of intracellular ALT, AST enzymes and alkaline phosphatase. Therefore, new domestic drug «Injectable Mevesel» created by us belongs to class 4 toxicity criteria, i.e. low-toxic substances.