Three major bovine herpesvirus type 4 (BHV-4) glycoproteins have been described previously. By using monoclonal antibodies produced against BHV-4 envelope proteins from which the three major antigens had been removed by immunoaffinity, a fourth glycoprotein was identified. This protein (gp1) has a high Mr (greater than 300K), is detected about 8 h post-inoculation of infected cells and is strictly expressed as a gamma protein. Moreover, gp1 was identified by a polyclonal antiserum from an infected animal, indicating that this glycoprotein is an antigen recognized by the immune system of infected animals.