Effects of the nootropic neuropeptide drugs cerebrolysin (Ebewe, Austria) and cortexin (Geterofarm, Russia) on the immunocompetent cells (T-lymphocytes of the MT-4 cell line and B-lymphocytes of the Raji cell line) were studied in vitro. The cell viability was evaluated using the MTT test by counting living and dead cells upon incubation under various conditions with a vital stain (Trypan Blue). It is established that cerebrolysin exhibits cytoprotective properties with respect to both T- and B-lymphocytes and favors the survival of immunocompetent cells. In addition, cerebrolysin in certain concentrations produces a proliferative effect on B-lymphocytes, thus stimulating the formation of immune memory B cells. In contrast, cortexin in certain concentrations produces a cytotoxic and antiproliferative action on T-lymphocytes. The parameters of influence for both drugs depend on their concentration in the cell incubation medium, the duration of action, and (most significantly) the cell type. These properties may account for one of the possible mechanisms of the immunoprotective action of cerebrolysin in various neurological states accompanied by immune response disorders.