Bovine herpesvirus type 1 (BHV-1) isolates are classified into 3 subtypes by use of restriction endonuclease analysis. Isolates from aborted fetuses have been either subtype 1 or 2a, whereas subtype 2b viruses have not been associated with abortion. We assessed the abortifacient property of isolates representing each of the 3 BHV-1 subtypes by IV inoculation of heifers with the virus 25 to 27 weeks after breeding. Three heifers were given Cooper (subtype 1) isolate, 3 heifers were given FI (subtype 2a) isolate, and 5 heifers were given K22 (subtype 2b) isolate. All heifers developed fever and viremia 2 to 5 days after inoculation. Heifers given Cooper or FI isolate aborted between 17 and 85 days after inoculation. The 5 heifers given K22 isolate delivered full-term calves. Placenta was obtained from 4 of the 5 heifers, and K22 virus was isolated from each placenta. Four calves had BHV-1 neutralizing antibody in precolostral serum, with titer ranging from 1:4 to 1:512.