Biotinylated DNA probes were constructed to hybndize with speclfic sequences within the messenger RNA (mRNA) of the nucleoprotein (N) gene of vlral hemorrhagic septicemia virus (VHSV) reference strains from Europe (07-71) and North Arnenca (Makah) Probes were synthesized that were complementary to (1) a 29-nucleotide sequence near the center of the N gene conlmon to both the 07-71 and Makah reference strains of the virus (2) a unique 28- nucleotide sequence that followed the open readng frame of the Makah N gene mRNA most of which was absent In the 07-71 strain, and (3) a 22-nucleobde sequence wthin the 07-71 N gene that had 6 nllsmatches \nth the Makah straln Sixteen dlverse isolates of VHSV from North Amenca and Europe were tested by dot blot hybridization The first probe reacted with all isolates of the virus the second probe reacted with only the North Amencan isolates (includng those from Pacific cod), and the third probe reacted with only the European isolates, Including those from rainbow trout brown trout and Atlantic cod The probes did not react with mRNA extracted from uninfected cells or from cells infected with infectious hematopoletic necrosls vlrus (IHNV) a related fish rhabdovlrus The results showed that VHSV isolates from North Amenca and Europe formed 2 genetically distlnct strains of the virus in which isolates from different years or species of flsh on each continent were more related to each other than to isolates from the other continent The results of this and other studies indicate that the North Amencan straln of VHSV is enzootic in the North Pacific Ocean and IS not a result of a recent importation of fish from Europe When used In conlunchon with a biotinylated probe that recognizes all isolates of IHNV, these reagents promse to slrnphfy the detechon of salmonid rhabdoviruses