The duration-of-immunity afforded by the ethylenimine inactivated rabies vaccine produced in BHK cells with the PV strain, was studied in dogs. One hundred per cent of the dogs became serologically positive 7 days after vaccination; the same percentage was still positive 3 years after vaccination with one dose of the vaccine. A good correlation was observed between the antibody profiles as determined by the titers obtained with the mouse neutralization and fluorescent field inhibition techniques. The correlation was not as good when the number of international units per ml was determined by both tests. The best correspondence between serological response and resistance to challenge was observed when the antibodies were determined by the number of international units per ml, using the neutralization test in mice. All the dogs challenged 12 and 25 months after vaccination resisted challenge; 89% (8/9) were protected 36 months after vaccination. Inactivated vaccines can be as effective to control rabies as those prepared with modified live virus; moreover, the inactivated vaccines are more stable and safer than the latter.