Adult rats were injected unilaterally into the anterior eye chamber and the submandibular gland with either [125I]tetanus toxin or [125I]nerve growth factor (NGF). Fourteen and 24 h later in electron microscopic autoradiographs of the superior cervical ganglia of the injected side the labeling was confined to a limited number (15-20%) of adrenergic ganglion cells and the silver grains were localized over axons, perikarya and dendrites providing evidence for a retrograde intraaxonal transport of the two macromolecules. Moreover, after injection of [125]tetanus toxin there was a very marked labeling of the presynaptic cholinergic nerve terminals. In contrast, after [125I]NGF these terminals were free of label. In both cases no specific labeling could be detected over glia and extracellular space. In the postganglionic axons the radioactivity seemed to be mainly associated with vesicles and smooth endoplasmic reticulum, in the perikarya and dendrites of the adrenergic neurons with secondary lysosomes, vesicles and smooth endoplasmic reticulum. The Golgi cisternae and the nuclei were free of radioactivity. The specific labeling of presynaptic terminals after injection of [125I]tetanus toxin together wirans-symaptic migration of [125I]tetanus toxin from the adrenergic ganglion cell to its innervating presynaptic terminals following retrograde intraaxonal transport.