This study was undertaken to prepare monoclonal antibodies which recognized the tegumental antigens of newly excysted metacercaria (NEM) and adult flukes of Paragonimus ohirai. From splenic cells of mice immunized with either the Triton X-100 extract of adult fluke surface or NEM sonicate, monoclonal antibodies were produced by ELISA screening followed by trial immunostaining of fluke sections. We prepared a monoclonal antibody (AS-Mab) recognizing the tegumental antigen of the adult fluke and a monoclonal antibody (MS-Mab) for the NEM tegumental antigen. AS-Mab also bound to the tegument of 1-week-old juveniles but not to that of NEM. MS-Mab bound the tegument from the metacercaria to adult stages, but the degree of immunostaining appeared to decrease with maturation of the flukes. By the double immunodiffusion technique, the two monoclonal antibodies formed crossing precipitin lines against a mixture of the adult surface antigen extract and the NEM antigen extract. MS-Mab and AS-Mab gave precipitin line against the incubation fluid from NEM and adult flukes, respectively.