Sindbis virus expression has been used for in vitro investigations of antigen processing, presentation and epitope mapping. The recent development of a replication-deficient recombinant Sindbis virus expression vector has made in vivo expression possible with minimal pathogenic risk. Advantages of Sindbis virus over other available viral systems include a comparatively smaller genome size making it possible to clone larger inserts, the ability to infect a wide range of host cell types with reduced pathogenicity for humans. These features suggest the possible utility of Sindbis virus for the in vivo delivery of genes to neural cells. We used the recombinant Sindbis viral expression system to target delivery of the lacZ gene to neuronal cells of mice by stereotactic surgery. Sindbis viral mRNA obtained by in vitro transcription was used to transfect baby hamster kidney (BHK) cells. As shown by histochemistry, beta-galactosidase (beta-gal) was expressed in approximately 50% of transfected cells. Cells were then cotransfected with DH-BB helper sequences that enabled the recombinant Sindbis virus RNA packaging. Nonreplicative Sindbis viral stock was collected 24 h after transfection. BHK cells were then infected with viral stock and histochemistry analysis was performed. Again, approximately 50% of the cells expressed beta-gal. The same viral stock was infused into the nucleus caudatus/putamen and nucleus accumbens septi and histochemical analysis of frozen sections from the relevant brain areas confirmed that beta-gal was expressed in neurons in a time-dependent manner. beta-Gal was detected at 24 h after inoculation and was present for at least 14 days, with maximum expression at 48 h. These results suggest that a nonreplicative Sindbis virus expression system may be useful for delivery of foreign genes into the central nervous system (CNS).