Reasons for dissatisfaction with insecticidal control of disease vectors include their presumed harmfulness to non-target organisms, their cost and difficulties of organizing effective spraying programmes and physiological and behavioural resistance in vector populations. The validity of these objections and possible ways of resolving them are discussed. The importance of assessing the actual field impact of cases where resistance has been detected with laboratory tests is stressed. With regard to behavioural resistance, some data are presented on tests for genetic variation in the tendency of mosquitoes to rest outdoors and hence to avoid contact with sprayed walls. Most of the failures of insecticidal control of vectors can be attributed, not to problems of resistance, but to organizational difficulties. The impregnation of mosquito bed nets with pyrethroids, which householders can do for themselves, is therefore being field tested in several parts of the world. Such impregnation makes nets effective even when they are torn. This method will probably be particularly advantageous against mosquitoes which enter houses to feed, but do not rest on walls.