Furthermore, the use of MoAb as the antigen-capturing antibody increased the specific binding of the PoAb, which could help to reduce the background and yielded very low detection limits of the assay, which are lower than those reported by Langley and Hillyer (1989) who used a sandwich ELISA for detection of F. hepatica ES antigens in serum samples of experimentally infected mice at a concentration 0.25 ng/ml.