A total of six ewes were intravenously inoculated at between 65 and 68 days of gestation with the Indiana strain of bovine viral diarrhoea virus (BVDV), containing both non-cytopathogenic (ncp) and cytopathogenic (cp) biotypes. Eight transplacentally infected fetuses were sequentially removed from the infected ewes and were found to have inflammatory lesions and malformations of the brain. BVDV RNA was isolated from formalin-fixed, paraffin-embedded brain tissue sections and detected by nested polymerase chain reaction after reverse transcription. The two biotypes of BVDV were distinguished by the fact that a sequence insertion in the RNA of the cp biotype of the inoculum results in larger amplicons. Only RNA from cp BVDV was detected in three of the brains removed up to 14 days post-inoculation (p.i.), and no BVDV RNA was detected after more than 14 days p.i. These findings suggest that, in critical phases of development, cp BVDV may transplacentally infect the ovine fetal brain and cause malformations.