Abstract: We compared the effect of a single dose of ivermectin (100ug/kg) with that of a standard course of diethylcarbamazine (DEC) (6mg/kg) on several parameters of the host's an-tifilarial immune response in 60 patients with bancroftian filariasis enrolled in a double-blind drug trial. All participants had measurable serum levels of antifilarial antibodies and parasite antigens. Drug-induced clearance of microfilaremia was associated with a temporary increase in HC11 antigenemia and a decrease in serum levels of antibodies to soluble filarial antigens. Antigenemia progressively declined in patients who remained amicrofilaremic after treatment, but declined and then rose in persons with recurrent microfilaremia. Treatment triggered a sustained increase in serum levels of IL-1 ,IL-6,TNFβ and IFNγ in all patients. Although Ivermectin and DEC are believed to exert their antiparasite activity via different mechanisms, the same pattern of serological changes was observed in patients treated with either drug.