The work described below forms part of an investigation to determine the residual toxicity of DDT when applied to the surface of materials commonly used in the construction of buildings. the bed-bug (Cimex lectularius, L.), because of its wide distribution and habit of infesting surfaces, either exposed or hidden, is an eminently suitable subject for such an investigation. In order to compare the residual toxicity of different surfaces after treatment with DDT, it was considered an essential preliminary step to ascertain whether or not the biological condition of the insect influenced its resistance to the insecticide. The present investigation was, therefore, undertaken to establish any possible variations in resistance which could be correlated with one or more of the following biological factors:— 1. starvation for different periods; 2. sex; 3. stage in the life-history; 4. temperature.