Abstract: 　AIM:To set up a simple immunoassay for the detection of circulating antigens in host serum. METHODS: A kind of colloidal pale purple dye (HFRL) used as a staining reagent for immunoassay was first selected from the dyes produced in China and an optimum condition for labelling the dye onto the combined IgM antibodies was explored. A dipstick sandwich colloidal dye immunoassay (DS DIA) for the detection of circulating antigens in host sera was established. RESULTS:The minimal concentration of SEA detected was 5 ng/ml by DS DIA. Serum circulating antigen detection in 14 cases of acute schistosomiasis japonica ,113 chronic cases and in 113 healthy controls revealed that the sensitivity was 100% in acute cases, 52.2% in chronic cases and the specificity was 92.9% for uninfected students.The sensitivity and specificity of DIA were similar to those of dot ELISA . A certain degree of diagnostic complementarity up to 76.1% in sera from these patients was seen when DS DIA and dot ELISA were used in parallel. CONCLUSION:DS DIA is a simple, economical and reliable method for detecting circulating antigens of Schistosoma japonicum ,having a wide potential value especially for field use.

Key words: Colloidal dye immunoassay (DIA), schistosomiasis japonica, circulating antigen detection