Abstract: A MS-ELISA using rabbit anti-microfilarial serum (RAS)-immunoglob ulins as the first antibody and monoclonal antibodies (McAbs) as the second antibody was developed for the determination of circulating antigens in human lymphatic fil ariasis. When McAbs against W. bancrofti microfilarial excretion-secretion antigens (ES-34) and against B. malayi L-3 antigen (HC-11) were used, a deteitability as little as 10 μg/ml and 50 μg/ml were achieved with positive rates of 94.5% (103/109) and 89.0% (97/109) respectively in microfilaremia patient sera (95 bancroftian, 14 brugia n) collected from India and Guizhou, China. A positive correlationship between antigen liters and circulating microfilaria density was observed with ES-34 MS-ELISA. However, in microfilaria-free cases of late stage with hydrocele, chyluria and elephantiasis complications, only 57.4% (31/54) and 61.1% (33/54) were obtained respectively with these two McAbs. Filarial antigens were also detectable in the urine in a part of the micr ofilaremia patients. 85 sera of healthy people collected from non-endemic areas in USA (36) and Guiyang, China (49) showed low positive rates of 0-4.1% with ES-34 and 2 .8-4.1% with HC-11. Negative reactions were observed in sera of all the 30 non-filaria cases harbouring intestinal helminths. The results strongly suggested that the presence of circulating antigens is correlated to the existence of active infections.