A population of 202 residents in an area endemic for Brugia timori lymphatic filariasis was treated in a diethylcarbamazine control programme commencing in 1977. All individuals were treated twice with diethylcarbamazine on a mass basis with additional selected treatment for cases with manifestations of infection. Clinical features of lymphatic filariasis were recorded annually until 1982, and the population re-assessed in 1988, six years after the completion of chemotherapy. Microfilarial counts were made on each occasion, and circulating filarial antigen levels measured for 1982 and 1988. The results showed a dramatic and sustained reduction in the rate of elephantiasis and adenolymphangitic disease, and of circulating antigenaemia, and the prevalence of microfilaraemia was reduced to zero by the end of the study.