Three West African strains of Anopheles gambiae Giles were intensively selected for DDT resistance at the adult stage using both mass selection and family selection with inbreeding. The LT50s for 4% DDT were thereby raised to 2–6 h, i.e. 6–18 × that of a susceptible strain. The selected strains were found to show DDT resistance as first-instar larvae and permethrin resistance as adults. The results of tests for the number of genes involved in causing the resistance and their linkage to genes for dieldrin resistance were equivocal. One of the DDT-resistant strains was bred in population cages with overlapping generations. Releases were made of males of the R70 translocation strain which transmit DDT and dieldrin susceptibility to their female progeny. When DDT selection on the cage population was relaxed, the releases caused a more rapid and complete loss of resistance than occurred in a control population. When selection for DDT resistance was applied to females of the cage population, the releases were able to prevent a build-up of resistance. The use of male releases is discussed as a possible means of countering insecticide resistance in mosquitoes.