Both p, p′DDT and a sample of commerical DDT have been compared with γ BHC as insecticides acting in the vapour phase. Both the direct fumigant action of the insecticides and the toxicity of the vapours sorbed on to stored products have been examined. After storage in atmosphere saturated with the vapours for six months, wheat retained sufficient of all three insecticides to control adults of Calandra graria (L.) and inhibit the develpment of larval Sitotroga ceraalella (Ol.). This control and inhibition was complete for BHC, and stronger for commercial than for p, p′DDT. Similar results were obtained when the insecticides sorbed on flour were tested using the eggs or larvae of Tribolium confusum Duv., or when fumigated groundnut kernels were tested against T. confusum, but such groundnut produced little toxic action against Oryzaephilus surinamensis (L.).