The sea bass, Dicentrarchus labrax, is one of the most extensively farmed marine fishes in the Mediterranean. Under the high-density condition common in aquaculture, the monogenean gill parasite Diplectanum aequans can cause significant economic losses. This study used real-time quantitative PCR to investigate the dynamic expression of immune response genes in sea bass infected with Diplectanum aequans. The target genes, interleukin-1 (IL-1b, transforming growth factor (TGF-b and T-cell receptor (TCR-b), were studied in the gills and spleen of the sea bass from the first day of infection until thirty days post- infection. Our results showed that there was an increase in IL-1b gene expression in the spleen and gills and in TGFb gene expression in the gills of infected fish. These results show that parasitic infection induced a local inflammatory reaction and that reaction was restricted to the site of infection. Finally, the absence of relationship between TCR-b expression and the parasitic infection suggests that the adaptive immune system is not involved in the response against this parasite.