Bioassays and binding tests between Cry toxins (Cry1Aa, Cry1Ab, Cry1Ac, and Cry2Ab) and brush-border membrane vesicles (BBMVs) from larvae of aBacillus thurningiensis (Bt)-susceptible (96S) and two Cry1Ac-resistant strains (BtR and LFR₁₀) were conducted for investigating cross-resistance of Cry1Ac-resistant strains to Cry2Ab inHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). The resistance ratio (RR) values of the BtR and LFR₁₀ strains to Cry1Ac and Cry2Ab were 2,971- and 1.1-fold and 253- and 1.0-fold, respectively, indicating that there was no cross-resistance to Cry2Ab. The binding experiments between Cry toxins and BBMVs from BtR, LFR₁₀, and 96S larvae showed that all of the toxins could bind with these BBMVs, but the Cry2Ab could not displace¹²⁵I labeled Cry1Ac and Cry1Ab. The same results were observed in reciprocal binding tests, demonstrating that Cry1A and Cry2Ab had different binding sites inH.armigera and providing a potential mechanism for the lack of cross-resistance between Cry1A and Cry2Ab toxins. These results suggest that the transgenic cotton,Gossypium hirsutum L., expressingCry1Ac andCry2Ab genes may be deployed for management of Cry1Ac resistantH.armigera.