The cytopathic (CP) strain TVM-2 of bovine virus diarrhea virus (BVDV) induced in calves a severe disease, whereas the calves inoculated with the non-cytopathic (NCP) New York-1 strain, remained clinically normal. When calves were immunosuppressed with dexamethasone (DMS) they underwent an overt, generally fatal disease. This result was obtained with either the CP and the NCP strain of BVDV. It was speculated that the immunosuppressive activity of BVDV could be a property peculiar to certain isolates of the virus.