The effectiveness of DDT applied to the walls of houses in interrupting the transmission of malaria by shortening the life of the Anopheles vector was the basis of national malaria programs until 1956, of the world malaria eradication campaign until 1968, and of the revised strategy of control or eradication until the present. Areas supporting nearly 800 million people, comprising most of the temperate-zone countries, have been thus liberated from malaria. The global incidence of malaria is now about 120 million cases annually, of which nearly 100 million are in tropical Africa; this may be compared with the estimate of 300 million annual cases before 1946, when the population was roughly 1/2 what it is in 1976. The principal problems in southern Asia, which is experiencing setbacks, are increasing insecticide-resistance in the vectors and a decrease in available funds in face of increasing operational costs.