Taurocyamine kinase (TK) was previously reported to be restricted to certain marine annelids; however, the present study has proven otherwise. The lung fluke Paragonimus westermani has a contiguous two-domain TK with a mass of 80216 Da consisting of 713 amino acid residues sharing higher sequence identity with molluscan arginine kinase (AK). Both domains of P. westermani TK have significant activity for the substrate taurocyamine and exhibited synergism during substrate binding. Since TK plays a key role in energy metabolism and is not present in mammals, inhibitors against P. westermani TK could be effective novel chemotherapeutic agents and could be utilized for the development of specific diagnostic tools for the detection of paragonimiasis.