Bovine herpesvirus type 4 (BHV-4), a member of the genus Rhadinovirus, subfamily Gammaherpesvirinae, within the family Herpesviridae, was isolated in fetal bovine lung cells from samples of vaginal discharge taken from a dairy herd in which approximately 50 per cent of the cattle developed metritis after calving. The identity of the isolate was confirmed by immunofluorescent staining with a BHV-4-specific monoclonal antibody and partial sequencing of a portion of the glycoprotein B gene. Serological testing failed to demonstrate a significant association between the exposure of the cattle to BHV-4 and the metritis, but several cattle seroconverted during the periparturient period, consistent with the recrudescence and shedding of virus associated with the stresses of parturition and the onset of lactation. Despite the previous failure to detect BHV-4 in Northern Ireland, a serological survey of 999 cattle in 49 dairy herds and 51 beef herds found widespread evidence of exposure: 29 of the dairy herds and 35 of the beef herds contained one or more seropositive cattle, and 33.3 per cent of the dairy cattle and 23.3 per cent of the beef cattle were positive.