The influence of temperature on the toxicity of the pyrethroids cypermethrin, permethrin, fenvalerate, d-phenothrin, flucythrinate and bioallethrin to 3rd instar Aedes aegypti larvae was determined. Based on LC50 levels, the toxicities of all pyrethroids were in the range of 1.33- to 3.63-fold greater at 20 degrees C than at 30 degrees C. Our laboratory results suggest that for larval control of Ae. aegypti, field performance of these pyrethroids may be reduced at warmer temperatures.