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Pre- and post-treatment temperature effects on -cyhalothrin toxicity were determined in insecticide-susceptible and resistant German cockroach, Blattella germanica (L.), strains. Acclimation at 19, 26, or 31C for 10 days before insecticide treatment had no effect on l- cyhalothrin toxicity in either strain. No differences were observed in aldrin epoxidase and glutathione S-transferase activities when “Orlando” (susceptible) cockroaches were incubated for 10 days at 19, 26, and 31C. When temperature treatment followed insecticide application, a negative temperature coefficient of toxicity (greater toxicity at lower temperature) toward l- cyhalothrin was observed for the Orlando but not the kdr-type resistant “Village Green” cockroaches. Piperonyl butoxide synergized l- cyhalothrin in “Orlando” cockroaches 3 and 5-fold at 26 and 31C, respectively. Conversely, piperonyl butoxide pre-treatment did not cause a significant reduction in the LD 50 value in the “Village Green” strain regardless of temperature.