NAD has been studied for its effect on the uptake of serotonin, norepinephrine, dopamine and GABA by synaptic vesicles. It has been shown that norepinephrine and dopamine uptake is not altered by addition of 10(-3) M, 10(-6) M, 10(-8) M, 10(-9) M and 10(-12) M NAD concentrations to incubation medium while the serotonin uptake is increased by 29, 47, 23, 24 and 18%, respectively. 10(-3) M and 10(-6) M NAD concentrations decrease GABA uptake by 30% and 24%. The study of 10(-6) M NAD effect on serotonin release from serotonin pre-loaded vesicles demonstrated the marked elevation of the neurotransmitter release, especially during the first 4 minutes of incubation (by 40%). The similar effect on serotonin release, is observed after addition of KCl, standard depolarizing agent, to the incubation medium. In contrast to synaptic membranes, the red blood cell membranes did not activate the neurotransmitter release after addition of serotonin pre-loaded vesicles to incubation medium, which proves the specificity of synaptic vesicles--synaptic membranes interaction. The modulating NAD action at the presynaptic membrane level can also be assumed.