A cDNA was isolated from a cDNA expression library using serum prepared against a high molecular mass fraction of Fasciola hepatica excretory-secretory products. The full-length cDNA encodes a member of the recently described peroxiredoxin antioxidant family. Peroxiredoxin could be the major hydrogen peroxide removing antioxidant in F. hepatica since this parasite does not express a catalase and expresses little glutathione peroxidase activity. This novel antioxidant may be involved in functions such as protection against reactive oxygen species (ROS) generated by metabolic processes and/or protection of the parasite against ROS released by immune effector cells.