Abstract: It is very important to evaluate the result in experiment using fluo-rescent retrograde neuronal label-ing technique that neurons could be labeled by the blood-borne fluo-rescent tracers.5 fluorescent tracers were injected intravenously into the tail veins of adult mice and rats.Injections of the tracers TB,FB and EB resulted in labe-ling of the somatomotor and vise-eromotor nuclei of the brain stem, the ventral horn of the spinal cord,the paraventricular nuclei of the hypotbalamus and the sensory ganglia.TB labeled neurons were seen in the sub-stantia nigra.Following i.v.injec-tions of NY and Bb,labeling oc-curred only in the sensory ganglia. The choroid plexuses,pin mater and the wall of the spinal central canal were labeled by all the tracers.