We have cloned and sequenced the M1 and M2 genes of both a European (virulent) and a North American (avirulent) strains of viral hemorrhagic septicemia virus, an important fish pathogen. We also compared the transcription of the two genes following infection of cells and determined the phosphorylation status and detergent solubility of the two proteins. Despite a total lack of homology with any available rhabdoviral sequence, the two VHSV proteins share comparable structural features with their respective VSV and RV equivalents. Thus, they are likely to exert similar functions. The amino acid sequence of both proteins is highly conserved between the European and the North American strains, indicating a probable common origin. The most remarkable features are that the virulent and avirulent strains differ in the location of the transcription start signal for the M2 gene and in TX-114 detergent solubility of the M2 protein. However, these differences are not paralleled with any observable change at the levels of M2 gene transcription, M2 protein expression, or virion maturation. Thus, they are unlikely to play a significant role in determination of the virulent status.