We evaluated the performance of Dot-enzyme-linked immunosorbent assays designed to detect species- and stage-specific antigens of Paragonimus westermani in sera with monoclonal antibodies as serodiagnostic tests for active paragonimiasis. Sera from all donors with parasitologically confirmed infections with P. westermani contained adult worm antigens, as did a high proportion of sera from persons suspected to be infected with this parasite. A smaller proportion of these sera also contained metacercarial stage-specific antigens. Sera from donors with other helminth infections, with confirmed pulmonary tuberculosis, or from healthy Chinese donors were nonreactive in the assay. Treatment of experimentally infected animals with praziquantel triggered a marked but transient increase in serum levels of adult P. westermani antigens, which then gradually disappeared within the next two months. The results of our studies indicate that the antigen-detection assay we have developed is a highly specific and sensitive diagnostic test for active infections with P. westermani.