Serological and genetical relationships of three salmonid herpesviruses [strain H-83, OO-7812 strain of Oncorhynchus masou virus (OMV) and Herpesvirus salmonis] were investigated. Although the serological relationships of these viruses were not distinctly demonstrated by cross-neutralization test, cross enzyme-linked immunosorbent assay revealed that strain H-83 and OMV appeared to be serologically more closely related to each other than to H. salmonis. Strain H-83 was genetically similar to OMV but distinct from H. salmonis by restriction endonuclease cleavage analysis and DNA-DNA hybridization test. These results indicated that strain H-83 should be classified under the same group as OMV, and H. salmonis belong to another group of salmonid herpesviruses.