The active principle, isolated from the funicles of A. auriculiformis, consisted of two triterpenoid saponins, acaciaside A and acaciaside B which killed in vitro 97% microfilaria of Setaria cervi in 100 min at 4mg/ml concentration and 100% of adults in 35 min. The drug, when administered orally at 100 mg/kg on rats, in which S. cervi adults were implanted intra-peritoneally, increased the blood mf count by 1.5-fold after the first phase of treatment for 10 days. Following the third phase of treatment and thereafter, the mf density was reduced by more than 80%. No toxic effect of the saponins was observed in rats. The rise in mf count indicated that the drug induced a very high physiological stress on the adult worms which increased the rate of discharge of the mf before impending death. The treated rats on autopsy did not show any adult worms.