15 monoclonal antibodies (McAbs) were induced with the neuropathogenic strain N 569 of bovine herpesvirus 1 type 3 (BHV-1.3). Nine of them could be shown by radioimmunoprecipitation assay to react with viral glycoproteins and two of these McAbs were able to neutralize strain N 569. The reactivity of these 15 monoclonals was compared with 11 monoclonal antibodies induced with a BHV-1.1 strain. The available monoclonal antibodies made it possible to characterize BHV-1.3 and to classify BHV-1 into three types, namely BHV-1.1, BHV-1.2 and BHV-1.3. This confirmed the results based upon restriction endonuclease analysis and viral protein patterns obtained earlier. The main antigenic differences of representative virus strains were found on two glycoproteins designated 3 and 12. Caprine herpesvirus 1, included in this study because of its serological relationship to BHV-1, differed fundamentally from BHV-1 on the grounds of McAb reactivity.