In order to study the antigenic structure of the G protein of VHSV, we produced several anti-G monoclonal antibodies (MAbs) and used 4 neutralizing MAbs (NMAbs) to select resistant (MAR) mutants. Each MAR mutant was confronted with the 4 NMAbs in a neutralization test, and also with our panel of MAbs in surface plasmon resonance (SPR) analysis to determine the extent of their relatedness. Determination of the sequence of the entire G gene of representative MAR mutants allowed us to map the mutations responsible for the resistant phenotypes. We identified several locations on the G protein sequence, which represent, most probably, critical positions within the binding sites of the neutralizing MAbs. In addition, the MAR mutants selected with a cross-reactive MAb exhibited a reduced pathogenicity for fish. This indicated that the regions bearing the point mutations selected with MAb C10 were probably involved in the determination of the virulent phenotype.