In vertebrate species, the MDM2 and MDM4 gene paralogs negatively regulate the activity of p53 family members and are involved in the development of a number of tumor types. Comparative genomic analyses have shown the presence of a single mdm homolog gene in invertebrates; its interaction with p53 and its involvement in tumor pathogenesis was demonstrated only in the mussel Mytilus trossulus. In addition to p53-related activity, a pro-inflammatory role for MDM2 in mammals has recently been described. In the present paper, we report the Real-time RT-PCR expression analysis of the mdm homolog gene in digestive gland tissue of Mytilus galloprovincialis collected from four different sites in the Campania region (Italy) during a single year. Our results revealed a positive correlation between the expression level of the mdm homolog and the percentage of chronic inflammatory lesions, both of which are increased during the summer period, suggesting a previously unidentified involvement of mdm in inflammatory processes in invertebrate species. Results obtained pointed out the potential interest of the use of mdm gene expression in marine food and seawater quality evaluation monitoring programs.