Herpes-like viruses have been reported last decades in various marine mollusc species in association with mortality outbreaks throughout the world (Renault & Novoa 2004). One of these viruses isolated during French outbreaks has been characterised as an unassigned member of the Herpesviridae family and named ostreid herpes virus 1 (OsHV-1) or Pacific oyster herpes virus (Davison et al. 2005). Studying anti-viral non-specific defence mechanisms (innate immunity) is of great interest, because they constitute the only one in molluscs. Therefore, innate immunity has be investigated in the Pacific cupped oyster, Crassostrea gigas. The main aim of the work was focused on the identification and the characterisation of genes induced by OsHV-1 in the Pacific cupped oyster. In turn, this could be of benefit to the control of viral diseases of mollusc species. Suppression Subtractive Hybridisation (SSH) has been used to characterize genes involved in anti-viral response using OsHV-1 and Pacific oyster as a disease model. The subtracted library was obtained using RNA from oyster haemocytes (control and after virus contact). Clones identified as differentially expressed using SSH were sequenced and compared to sequences available in databases. Of the clones showing homology with known genes, several of them have functions connected to the innate immune response : macrophage expressed protein, molluscan defense molecule precursor or laccase 1. The full-length cDNA of these three genes was obtained using 5' and 3' RACE PCR. The predicted amino sequences were analysed for domain features and conserved signature motifs (Smart). Multiple alignment (ClustalW) and homology analysis of the deduced amino acid sequences of laccase 1, molluscan defence molecule precursor and macrophage expressed protein gene homologues were carried out. A phylogenic analysis was performed with MEGA program (version 3.1) based on amino acids alignment. The expression pattern of transcripts in healthy and OsHV-1 challenged oysters was studied by RT qPCR for laccase, molluscan defence molecule precursor and macrophage expressed protein gene homologues. The expression of the three selected genes was up-regulated and reached a maximum 48 hours after OsHV-1 challenge.