The impact of annual single-dose community-wide treatment on the transmission of Wuchereria bancrofti was investigated in 5 villages in the East Sepik Province where pretreatment prevalence of microfilaraemia ranged from 34% to 73%. Anopheles punctulatus and An. koliensis were the only carriers of the parasite. 3 villages received diethylcarbamazine citrate (DEC) in combination with ivermectin (IVR) and 2 received DEC alone. The rate and intensity of microfilaraemia were both reduced in all 5 villages. Reduction in prevalence was between 43% and 67% in the DEC+IVR study villages and between 24% and 27% in the DEC alone villages. Density was reduced by between 81% and 95% in the DEC+IVR villages and between 69% and 74% in the DEC alone villages. Breaks in perennial transmission (failure to detect infective mosquitoes in four or more consecutive monthly collections) occurred in all 3 communities treated with DEC+IVR. Transmission was almost completely interrupted in 2 villages, where infective mosquitoes were not detected during 11 of the 12 months following treatment. We concluded that repeated annual single-dose community-wide treatment with DEC+IVR could lead to complete interruption of transmission and ultimately elimination of lymphatic filariasis.