We studied the effect of transplantation of splenic lymphoid cells on functional activity of the nervous (orientation and exploratory behavior and expression of genes for interleukin-1beta, type 1 interleukin-1 receptor, and erythropoietin in the brain) and immune system (cellular and humoral immune response, proliferative activity of immunocompetent cells, and expression of cytokine genes in splenocytes) in syngeneic animals with different behavioral characteristics. Intravenous injection of the lymphoid fraction of splenocytes from donor mice with a certain behavioral pattern in the open-field test had a modulatory effect on vertical locomotor activity of syngeneic recipient mice. The increase or decrease in vertical locomotor activity due to transplantation of immunocompetent cells was accompanied by specific changes in mRNA level for erythropoietin receptor and type 1 interleukin-1 receptor in brain cells of recipient mice. The regulation of orientation and exploratory behavior was also accompanied by changes in functional activity of the immune system in recipient animals. It was manifested in modulation of proliferative activity of thymic and splenic cells and cytokine gene expression in splenocytes.