The method of retrograde axonal transport of horseradish peroxidase was used to study the organization of the projections of the morpho-functional system of the basal ganglia nuclei to the individual substructures of the of deep mesencephalic nucleus complex (DMNC) of dog brain (n = 9). It was found that the nucleus accumbens was the only striatum structure containing the neurons that sent projection fibers to the subcuneate nucleus. The projections of the output structures of the basal ganglia--pallidum, substantia nigra, zona incerta, pedunculopontine nucleus were more numerous in DMNC. It was demonstrated that not all DMNC substructures received projection fibers from the neurons of all the nuclei of the basal ganglia structures mentioned. Thus, the fibers from the neurons of the globus pallidus and the ventral pallidum innervated the cuneiform and the subcuneiform nuclei, while those from the entopeduncular nucleus projected to all the DMNC substructures. The projection fibers from the zona incerta neurons were directed to the subcuneate nucleus and to the deep mesencephalic nucleus, while those from the pedunculopontine nucleus projected to the cuneate and the subcuneate nuclei. The projections from the substantia nigra neurons were directed to all the substructures of DMNC.