The excretory/secretory (ES) materials from filarial parasites form an important tool for immunodiagnosis of filariasis. We have raised monoclonal antibodies against ES proteins isolated from the medium incubated with live adult bovine filarial parasite Setaria digitata. The hybridoma were cloned and characterised with respect to the individual proteins of the ES materials. A secretory glycoprotein with molecular weight 200-kDa (gp200) was purified, localised and characterised using the specific monoclonal antibodies raised against it. The immunolocalisation study clearly showed that the protein is secreted out through the pores on the surface of both male and female parasites. The gp200 on reduced sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed dissociation into 11- to 66-kDa 'ladder' polypeptides, and all of them could be identified with the same monoclonal antibody. The gp200 is normally shed along with the ES materials. The screening of human sera samples using the monoclonal antibodies give promising results which showed that gp200 could be a potent candidate protein for the immunodiagnosis of filariasis by the method of antigen detection.