Monoclonal antibodies (MAbs) specific to the lung fluke (Paragonimus heterotremus) were produced against the soluble metabolic products (excretory-secretory antigen). Three hybrids secreting MAbs specific for P. heterotremus antigens were identified by an indirect enzyme-linked immunosorbent assay (ELISA) against a panel of homologous and 24 heterologous parasite antigens and Mycobacterium tuberculosis. Of the three specific clones, clone 10F2, which was IgG1 producing and which gave immune complex bands with 31.5-kD and 22-kD polypeptides by gel electrophoresis and immunoblotting, was selected for further characterization and evaluation of its possible diagnostic potential. The result obtained from an indirect immunofluorescent antibody test suggested that MAb 10F2 reacted with mucosa and contents of the worm's intestine. The antibody could be readily used to prepare an affinity-purified antigen for use in an indirect ELISA that was highly sensitive and specific for the detection of circulating antibody in sera of paragonimiasis patients.