The author reviews the distribution, epidemiology, and treatment of filarial infection due to Brugia malayi, with special reference to Malaya. B. malayi infection in man is confined to the Far East between longitudes 75 degrees E and 140 degrees E and is essentially rural. The chief vectors are Mansonia spp., Anopheles hyrcanus group, A. barbirostris group, and Aëdes togoi. The epidemiological picture is complicated by the fact that B. malayi and other closely related species have now been found in several species of animals. The existence of an animal reservoir of infection might have important implications for filariasis control. As to the treatment of B. malayi infection, diethylcarbamazine has been found to reduce the microfilaria count and to kill the adult worms; the severe febrile reactions of microfilaria carriers to the initial doses of this drug may be reduced by administration of the steroid prednisolone.