Abstract: Objective To prepare specific antibodies against the recombinant Em18 antigen （ReEm18）， estab-lish a sandwich ELISA and detect the Em18 circulating antigen in patients^, sera. Methods Rabbits and BALB/c mice were immunized with the ReEm18 antigen， which was purified by affinity method for preparation of the specific poly-clonal and monoclonal antibodies. A sandwich ELISA was established by the specific antibodies. Results By immu-nizing with the ReEm18 antigen， high antibody level was reached with a serum dilution of 1 ∶ 204 800 and above in the immunized rabbits. After double selection by ELISA using the ReEm18 antigen and block ELISA using both AE-positive and negative control sera， 14 positive cell clones were obtained with an inhibition rate of more than 50%. Those mono- and poly-clonal antibodies were matched freely in sandwich ELISA tests for detecting the ReEm18 antigen. A combina-tion of monoclonal antibody No.9 and polyclonal antibody showed the best result. The sensitivity to detect ReEm18 anti-gen was at 3 ng/ml. Six of 11 AE sera were positive when tested with the sandwich ELISA system. Conclusion Highly specific polyclonal and monoclonal antibodies have been prepared， and a sensitive sandwich ELISA established. Preliminary result is suggested that a detectable level of Em18 circulating antigen is present in AE patients^, sera.

Key words: Alveolar echinococcosis, Em18 recombinant antigen, Antibody, Circulating antigen, Sandwich ELISA