AbstractStructure‐activity relationships were examined in toxicological studies with DDT‐type insecticides. The Taft σ* parameter for the electronegative character of substituents correlated well with the uptake of the analogs through insect tarsi and with acute oral toxicities to mice. Substituent groups with stronger electron‐withdrawing capacities penetrated more slowly through the insect cuticle and were markedly more toxic to mice. A nuclear magnetic resonance method was utilized to obtain estimated σ* values for use in the corre