Adenoviral vectors have recently been recognized as highly efficient systems for gene delivery into various tissues. We show that a reporter gene introduced into nerve terminals via an adenovirus can be used to label cell bodies retrogradely and then label the axons and nerve terminals of the infected neurons anterogradely in vivo. We injected a replication-defective recombinant adenovirus carrying the E. coli beta-galactosidase gene (lacZ) into the cerebellar cortex of the adult mouse. The first evidence of retrograde labeling was obtained at 2 days after the infection when neurons in the pontine nuclei and the reticulotegmental nucleus of the pons weakly expressed beta-galactosidase, and at 3 days post-infection when neurons in all precerebellar nuclei, known to project to the cerebellar cortex, were strongly stained with X-gal in a Golgi-like manner. Anterograde transport of lacZ gene products was recognized at 3 days post-infection; beta-galactosidase-positive axons arose from somata or dendrites of retrogradely labeled neurons, passed through the middle or inferior cerebellar peduncles, and entered the cerebellum. Anterogradely labeled mossy terminals were recognized on the injection side at 8 days post-infection, and on the contralateral side at 14 days post-infection. Beta-galactosidase expression persisted for up to two months, with a decrease in the total number of labeled cells over time. We could not find any signs of anterograde or retrograde transsynaptic labeling in the nuclei synaptically linked to the cerebellar cortex at any time point after injection up to 58 days post-infection.