In DDT-treated American cockroaches, Periplaneta americana (L.) (Orthoptera: Blattidae), glycogen and trehalose concentrations were lowered over a relatively short time span corresponding to the period from late hyperactivity to early prostration. Such a depletion did not occur in DDE (l,l,dichloro-2,2-bis(p-chlorophenyl) ethylene)-treated insects. This depletion corresponded with a peak in 14CO2 evolution from cockroaches receiving glucose-14C injections. The depletion occurred even when supplemental injections of up to 6 mg trehalose per cockroach were made, but was delayed by a rise in temperature. Dieldrin and propoxur poisoning caused a similar carbohydrate depletion. Carbohydrate depletion is proposed as a link between the effect of DDT on the nervous tissue and the response of the rest of the tissues of the insect.