The immunoregulating effect of phenibut has been demonstrated on the model of immune stress caused by the injection of lipopolysaccharide from Pseudomonas aeruginosa. The degree of expression of the specific (in a delayed-type hypersensitivity reaction and passive hemagglutination) and nonspecific (phagocytic activity of neutrophils) links of immunomodulation was studied. The formation of lipopolysaccharide (LPS) induced immune stress is characterized by the increase of the indicated parameters of immunity. It is found that phenibut (under intraabdominal injection of 25 mg/kg within 5 days) removes the manifestations of hyperreactivity of the cellular link of immunity, and also restores the amount of phagocytic cells, which is evidence of the immunomodulating properties of the drug under conditions of hyperimmunization.