Herpesvirus infections of kokanee salmon, masu salmon, coho salmon, and rainbow trout have been reported in Japan. The 11 herpesvirus strains isolated from kokanee salmon (NeVTA), masu salmon (YTV and 3 strains of OMV), coho salmon (CSTV, COTV and 2 strains of OKV), rainbow trout (RKV and RHV), and Herpesvirus salmonis were compared for their serological relatedness by serum cross-neutralization tests with polyclonal rabbit antiserum. The herpesvirus strains isolated in Japan were neutralized by antisera against these viruses and were found to be closely related to salmonid herpesvirus 2 (OMV strain 00-7812). These strains were, however, clearly distinguished from salmonid herpesvirus 1 (H salmonis).