There has been little change since 1955 in the laboratory techniques for seeking new antifilarial compounds, although one valuable addition to laboratory study has been the experimental infection of cats with Brugia malayi.The chief drug for the treatment and control of filariasis-whether caused by Wuchereria bancrofti or by B. malayi-continues to be diethylcarbamazine, and the author reviews the reports recently published on its use. In India and China large-scale campaigns involving the use of this drug have been undertaken; and in Tahiti filariasis has been suppressed and almost eliminated. Campaigns on a smaller scale and pilot projects considered in this survey include those conducted in Pacific islands, Malaya, Ceylon, Brazil, Surinam and East and West Africa.It is generally agreed that the administration of diethylcarbamazine produces a great diminution in the microfilarial counts of those taking it, and in many persons both microfilariae and adult worms are eradicated. The difficulties which arise are due to toxic effects which occur in some recipients and which may adversely affect the acceptability of treatment.