It has long been stressed that diethylcarbamazine citrate must be given at a total dosage of 72 mg/kg of body weight in 12 divided doses of 6 mg kg - 1 to obtain maximum effect against Wuchereria bancrofti. However, recent studies revealed that only a single dose at 6 mg kg - 1 could reduce microfilaria (Mf) counts by 90%, and that the effect would persist for 12-18 months. The annual repeat of the single-dose mass treatment was shown to be effective in reducing Mf prevalence and density in large-scale, long-term field trials. The scheme is simple and economic, and could be sustainable in many endemic areas, where health manpower and resources are often not sufficient. Annual single-dose mass treatments can be an effective weapon against human lymphatic filariasis, as discussed here by Eisaku Kimura and Jona Mataika.