A night blood survey was carried out among inhabitants aged over 1 year from the fifteen villages throughout Cheju-Do (Quelpart Island). Blood films from 2,139 persons were examined and 183(8.6 percent) showed microfilariae, the incidences varying according to geographical sources are from 0.8 to 19.5 per cent. All the microfilariae found in this survey were of the nocturnal periodic Brugia malayi. The microfilarial density was 1.9 per cent of blood. The age and sex distributions of microfilaria rate in Cheju-Do were not distinctly different. On the other hand, the intradermal test using Dirofilaria antigen (FPT antigen) and clinical survey of filariasis were also undertaken in same areas of microfilaria survey. Out of 2,449 inhabitants examined 1,434(58.6 percent) persons showed positive reaction of skin test, 503(20.5 percent) persons have clinical manifestations and 112 (4.6 percent) persons showed elephantiasis . It is assumed that Aedes togoi may be the most probable vector of B. malayi in the areas of Cheju-Do.
