The Manila clam, Ruditapes philippinarum, is an economically-important, commercial shellfish; harvests are diminished in some European waters by a pathogenic bacterium, Vibrio tapetis, that causes Brown Ring disease. To identify molecular characteristics associated with susceptibility or resistance to Brown Ring disease, Suppression Subtractive Hybridization (SSH) analyzes were performed to construct cDNA libraries enriched in up- or down-regulated transcripts from clam immune cells, hemocytes, after a 3-h in vitro challenge with cultured V. tapetis. Nine hundred and ninety eight sequences from the two libraries were sequenced, and an in silico analysis identified 235 unique genes. BLAST and "Gene ontology" classification analyzes revealed that 60.4% of the Expressed Sequence Tags (ESTs) have high similarities with genes involved in various physiological functions, such as immunity, apoptosis and cytoskeleton organization; whereas, 39.6% remain unidentified. From the 235 unique genes, we selected 22 candidates based upon physiological function and redundancy in the libraries. Then, Real-Time PCR analysis identified 3 genes related to cytoskeleton organization showing significant variation in expression attributable to V. tapetis exposure. Disruption in regulation of these genes is consistent with the etiologic agent of Brown Ring disease in Manila clams.