NGF is produced in the olfactory bulb and transported from the bulb to cholinergic neurons in the horizontal limb of the diagonal band. Although the expression of NGF receptors has been reported in olfactory epithelial cells, no correlation between NGF and olfactory epithelial cells has been found. This study aimed to define whether or not retrograde transport of NGF occurs in the olfactory neural system using the method of radioluminography.125I-labeled NGF injected into the olfactory bulb was taken up and transported to the olfactory epithelium 18 h after injection. This finding suggests that bulbar NGF may act as a neurotrophic factor in olfactory epithelial cells.