The adult vial test (AVT) was used successfully to monitor for resistance to nonpyrethroid insecticides in field populations of tobacco budworms (TBW). Resistance was present in Texas and Arkansas in 1993, but the frequency decreased compared to 1992. The seasonal pattern of resistance in 1993 was similar to that of 1992 in that resistance frequency declined late in the season. The lack of synergism of profenofos by PBO and the difference in AChE inhibition by a phosphate (7-fold) and a carbamate (9-fold) between resistant and susceptible TBW indicated that target site insensitivity is the major mechanism of resistance to organophosphate (OP) and carbamate insecticides. Cross-resistance of TBW to endosulfan and dieldrin, lack of significant increase in toxicity of endosulfan with PBO or DEF, and high correlation (r > 0.98) of the toxicity of both insecticides indicated similarity of the mechanisms of resistance to them. Measurement of penetration, excretion and total metabolism of radiolabelled profenofos indicated that a change in cuticular permeability might be a complementary resistance factor in the TBW.