A comparison of the DNA homologies between five salmonid herpesviruses showed two distinct groupings. Herpesvirus salmonis (HPV) and the steelhead herpesvirus (SHV) appear to be different strains of the same virus. Oncorhynchus masou virus (OMV) andyamame tumor virus (YTV) also appear to be different strains of the same virus, althoughnot as closely related to one another as SHV and HPV. The nerka virus (NeVTA) issimilar yet distinct from OMV and YTV. It appears that the salmonid herpesviruses canthus be classified as follows;Herpesvirus salmonis Type 1 (HPV and SHV, from NorthAmerica) and Herpesvirus salmonis Type 2 (OMV, YTV and NeVTA, from Japan).