To achieve gene delivery to sensory neurons of the trigeminal ganglion, thymidine kinase-negative (TK-) herpes simplex viruses (HSV) containing the reporter gene lacZ (the gene for E. coli beta-galactosidase) downstream of viral (in vectors RH116 and tkLTRZ1) or mammalian (in vector NSE-lacZ-tk) promoters were inoculated onto mouse cornea and snout. Trigeminal ganglia were removed 4, 14, 30, and 60 days after inoculation with vectors and histochemically processed with 5-bromo-4-chloro-3 indolyl-beta-galactoside (X-Gal). With vector tkLTRZ1, large numbers of labeled neurons were observed in rostromedial and central trigeminal ganglion at 4 days after inoculation. A gradual decline in the number of labeled neurons was observed with this vector at subsequent time points. With vectors RH116 and NSE-lacZ-tk, smaller numbers of labeled neurons were seen at 4 days following inoculation than were observed with vector tkLTRZ1. No labeled neurons could be observed at 14 days after inoculation with vectors RH116 and NSE-lacZ-tk. Immunocytochemistry for E. coli beta-galactosidase and in situ hybridization to HSV latency-associated transcripts revealed labeled neurons in regions of the trigeminal ganglion similar to that observed with X-Gal staining. A comparable distribution of labeled neurons in trigeminal ganglion was also observed after application of the retrograde tracer Fluoro-Gold to mouse cornea and snout. These data provide evidence that retrogradely transported tk- herpes virus vectors can be used to deliver a functional gene to sensory neurons in vivo in an anatomically predictable fashion.