WE have recently been able to examine the absorption and metabolism of benzene hexachloride by susceptible and γ-BHC-resistant strains of Anopheles gambiae. The resistant strain, which originated in an area of northern Nigeria where dieldrin is being used as a residual spray1, was dispatched to England by members of the Nigerian Malaria Service and has been reared in the laboratories of the Ross Institute, London, by Dr. G. Davidson, who has kindly supplied the insects for our experiments. The resistant strain is some 800 times resistant to dieldrin and 26 times resistant to γ-BHC as determined by Davidson2 using a modification of the method of Busvine and Nash3. The susceptible strain has also been reared in the laboratories of the Ross Institute in London and originated from Lagos, Nigeria.