For many years the World Health Organization has been engaged in a programme for the control of vector-borne diseases, and in 1960 established a programme for evaluating and testing new insecticides, the special objectives being to find new compounds that would overcome the problem of insecticide resistance and not lead to further contamination of the environment.This paper reviews the present status of control of some of the principal vector-borne diseases of man and describes the WHO programme for insecticide evaluation and testing and the results it has achieved.