IR162 is a rat monoclonal IgE antibody (mAb). In the investigation of rat IgE production, the antigens recognized by IR162 (IR-Ags) were found to be expressed by a variety of helminthic parasites. By western blot analysis, IR162 detected bands in crude extracts of Anisakis simplex larvae, Clonorchis sinensis, Paragonimus westermani, plerocercoids of Spirometra mansoni, and Toxocara canis. Excretory–secretory material from A. simplex larvae also contained a protein recognized by IR162. IR162 mAb obtained from both Serotec and Zymed recognized identical bands of A. simplex larvae. Sandwich enzyme-linked immunosorbent assay analysis indicated that both IR-Ags of A. simplex larvae (IR-As) and C. sinensis (IR-Cs) were important antigens with respect to induction of specific IgG in human infections with these 2 organisms. Even though minimal cross-reaction between IR-As and IR-Cs was observed using sera from infected individuals, these results indicate that IR-Ags are found in the parasites examined, that IR-As and IR-Cs are the antigens that induce specific antibody in natural infection, and that the epitope that binds IR162 is shared by A. simplex larvae and C. sinensis.