Bioassays of the pyrethroids permethrin, fenvalerate, cypermethrin, biphenate, cyhalothrin and deltamethrin against laboratory strains of bollworms and tobacco budworms indicated no differences in susceptibility between the two species. LD-50 values for all of the pyrethroids fell in a narrow range which was significantly lower for both species than LD-50 values determined for methyl parathion, profenophos, and methomyl. Field strains of tobacco budworms collected in Louisiana, Texas, Arizona, and Mississippi during 1985 and 1986 exhibited moderate to high levels of resistance to fenvalerate (2-35X), permethrin (1-74X), and cypermethrin (2-9X). A 2-fold reduction at the LD-50 level and a 13-fold reduction at the LD-90 level in resistance to fenvalerate were observed in a highly resistant strain of the tobacco budworm from the F1 to the F2 generation reared in the laboratory without any selection pressure.