In order to develop a serodiagnostic assay to detect antigens of Paragonimus westermani in biological specimens, we generated monoclonal antibodies to antigens of metacercariae and adult worms, and partially characterized the epitopes recognized by representative Mabs. Metacercarial stage-specific determinants were periodate-sensitive and protease-resistant, indicating that they are carbohydrate epitopes. In contrast, adult worm-specific determinants resisted periodate treatment but were sensitive to proteases, indicating that they are polypeptides. The majority of cross-reactive Mabs studied were directed against phosphorylcholine determinants. When used in a dot-ELISA, Paragonimus-specific Mabs could detect 0.3–7 ng/ml parasite antigen in human sera.