Studies have shown that the American cockroach, Periplaneta americana, undergoes physiological and biochemical changes in response to temperature treatments. One objective of the research described in this dissertation was to determine if the temperature regime before or after treatment affects the toxicity of allethrin to the American cockroach. Insects were acclimated for 7-8 days at 14°, 22°, or 30° C, treated by immersion, then held at one of the same 3 temperatures until mortality determination. Acclimation at low temperature resulted in up to a 3-fold increase in toxicity to adult males. When the effects of low post-treatment temperature were combined with low acclimation temperature, a 24-fold increase in toxicity occurred;Another objective was to determine if acclimation temperature affects lipid composition of nerve cords or fat bodies in P. americana. These studies were done because other workers have suggested that lipid changes are important to toxicity. Gas-liquid chromatography of lipid extracts detected 15 fatty acids in nerve cords and 17 in fat bodies; 11 of these were identified in each organ. The predominant fatty acids detected in nerve cords and fat bodies, respectively, were oleic (40%, 40%), palmitic (22%, 25%), linoleic (17%, 18%), and stearic (10%, 10%) acids;Nerve cords and fat bodies responded quite differently to a one-week period of temperature acclimation. Low temperature acclimation resulted in an orderly increase in weight-% of 3 unsaturated fatty acids and a decrease in 3 saturated fatty acids in nerve cords. Changes in fat body lipids, however, followed no consistent pattern. No direct evidence linking neural lipid changes with toxicity changes is presented in this research. However, low acclimation temperature resulted in increased unsaturation of nerve cord lipids and increased toxicity of the neurotoxin allethrin; the significance of this correlation is discussed.