A herpes simplex virus (HSV) vector in which the mammalian promoter for neuron-specific enolase (NSE) controls expression of a marker gene was analyzed for its ability to drive expression of this foreign gene in culture and in vivo. In cultured cells, the vector appeared to give neuron-specific expression. Introduction of 10(6) pfu of the virus into the adult rat caudate nucleus by stereotactic injection was not toxic to the animals and yielded beta-galactosidase (beta-gal)-positive neurons for at least 30 days after viral inoculation. This recombinant herpes virus vector is the first described to use a mammalian promoter to yield extended expression of a foreign gene product in the adult mammalian central nervous system (CNS).