To test the safety and efficacy of a thymidine kinase-negative (TK-), temperature-resistant (TR) mutant of bovine herpes virus-1 (BHV-1) in pregnant cows, seronegative cows, 2-5 months pregnant, were vaccinated intramuscularly (i.m.) or intravaginally (i.vag.) with this candidate vaccine virus. I.m. vaccinated cows did not shed virus i.vag. or intranasally (i.n.), but i.vag. vaccinated cows replicated virus i.vag. for 8-9 days postvaccination (p.v.) Some of the cows were challenge exposed i.n. at 46 days p.v. with virulent TK+ BHV-1(Cooper). Vaccinated cows showed no clinical disease signs p.v. or postchallenge and responded anamnestically postchallenge. All cows delivered live calves. Pre-colostrum sera of the calves were negative for BHV-1 antibodies.