Isolates of herpesvirus type 2 from different geographic areas were examined for antigenic differences using the kinetics of neutralization and 51Cr release tests. Though differences in the kinetics of neutralization between strains were observed, the 51Cr release test appeared to provide better discrimination of strains. The results of 51Cr release assays using adsorbed sera suggest that 2 subsets of type 2 strains may exist which were tentatively called α and β. Members of subset α appear to have an antigen exposed on the surface of infected cells which is qualitatively or quantitatively expressed to a lesser degree on cells infected with subset β viruses. In the limited number of strains tested, hamster cells transformed by subset α viruses were oncogenic when injected into hamsters while cells transformed by subset β viruses were not.