A monoclonal antibody (designated 8SE) against membrane antigen of adult Schistosoma japonicum labeled with HRP was used in dot-ELISA (direct method) to detect schistosomal circulating membrane antigen. Sera from 48 parasitologically confirmed schistosomiasis cases were tested, 39 (81.3%) were positive. No false positive reaction was found in sera from 24 healthy controls. No cross reaction was detected in sera from clonorchiasis or paragonimiasis in 18 cases each. This results suggest that circulating membrane antigen does exist in patients with schistosomiasis and it might be used as a complementary method for diagnosis of schistosomiasis. A preliminary result of idiotype/antiidiotype interaction inhibition reaction for detecting circulating membrane antigen was also presented.