The present study evaluates the interactions between Philasterides dicentrarchi, a ciliate parasite that causes high mortalities in cultured flatfish, and turbot (Scophthalmus maximus) peritoneal cells during an experimental infection. The transcriptomic response was evaluated in parasites and in turbot peritoneal cells at 1, 2, 4, 12 and 48 h after intraperitoneal injection with the parasite