Immunomodulatory effects of piracetam and a number of its derivatives were studied in mice. It was shown that multiple injections of such substances at a dose of 50-200 mg/kg change the amount of antibody-forming cells in the spleen of animals immunized with sheep red blood cells. The dose of 200 mg/kg was the most effective one, with the direction of immunomodulatory activity depending on the chemical composition of the compounds. Thus joining of phenol radical to piracetam molecule strengthened immunosuppression, and vice versa insertion of hydrazide group led to stimulation of antibody formation. It is stressed that immunosuppressive effect of piracetam must be taken into consideration during the clinical use of the drug.