Monoclonal antibody-based enzyme-linked immunosorbent assay and DNA dot blot hybridization techniques were developed and evaluated for their potential in the detection of Opisthorchis viverrini. A mixture of IgG monoclonal antibodies specific for the 89 kDa metabolic product of O. viverrini was captured on a microtiter plate by rabbit anti-mouse IgG and used in a sandwich ELISA for the detection of soluble parasite antigen in the feces of patients with opisthorchiasis. As little as 0.1 ng of the antigen could be detected. A specific O. viverrini DNA probe was used in a dot blot hybridization of parasite DNA. The labeled probe could detect DNA released from as few as five O. viverrini eggs. Both approaches were highly specific for O. viverrini and their sensitivity appeared to be comparable with that of the classical parasitological method. Preliminary data obtained from a field trial showed that these two methods have potential in the diagnosis of opisthorchiasis. Moreover, the limited data currently available showed that it is possible to use these methods to detect the presence of O. viverrini metacercariae in naturally infected fish.