The vestimentiferan annelidRiftia pachyptilaforms dense populations at hydrothermal vents along the East Pacific Rise at a depth of 2600 m. It harbors CO2-assimilating sulfide-oxidizing bacteria that provide all of its nutrition. To find specific host transcripts that could be important for the functioning of this symbiosis, we used a subtractive suppression hybridiza-tion approach to identify plume- or trophosome-specific proteins.