Antigenic patterns of BHV-1 isolates from Argentina, Chile and Brazil were examined with a panel of monoclonal antibodies (MAbs) generated with BHV-1.1 and BHV-1.3 strains. Among the Argentinian isolates, 7/8 neurological cases showed BHV-1.3 characteristics and 10/12 non-neurological cases from all countries exhibited BHV-1.1/2 pattern. All viral isolates from genital infections showed BHV-1.1/2 characteristics. Chilean isolates exhibited BHV-1.1/2 pattern and one among 3 Brazilian viruses was defined as belonging to BHV-1.3. Results of the characterization using MAbs, were confirmed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of representative isolates. A total correlation was observed between the reactivity with MAbs and the SDS-polyacrylamide analysis. Based on the data presented, it is concluded that the type 1.3, most frequently obtained from the brain of neurological cases, is present in Argentina and Brazil and coexists with BHV-1.1/2.