The effects of substance P (SP) and its new structural analog EC-1 administered systemically to CBA mice on the immune responsiveness have been examined. Three main findings are presented in this study. First, the principal effect of SP and EC-1 on the immunity is a stimulatory one. It is shown that in the doses of 1, 10 and 100 mkg/kg of the body weight both neuropeptides significantly increased the number of plaque- and rosette-forming cells in the spleen of animals at the peak of the immune reactions. Second, the destruction of the pituitary stalk prevented the immune response stimulation caused by neuropeptides. Third, SP-induced immunostimulation was not observed after combination with the antagonist of the postsynaptic dopamine (DA) D-2 receptors haloperidol (2 mg/kg) suggesting the involvement of the DAergic system in the realization of this effect. Thus, these results demonstrate neurochemical DAergic mechanisms underlying the immunostimulating influence of tachykinins.