Transgenic cottons expressing either one or two Bacillus thuringiensis Berliner proteins, along with the conventional sister line, were evaluated in a 2001 field experiment with regard to impact on bollworm production in North Carolina. The relative numbers of bollworms that were capable of successfully completing development on Bollgard^® II, Bollgard^®, and conventional cottons under insecticide-sprayed and unsprayed conditions were estimated. Bollgard and Bollgard II genotypes were highly successful in the reduction of bollworm larvae on a per acre basis when compared to the conventional variety. Utilization of a pyrethroid insecticide for bollworm control also significantly reduced numbers of bollworm larvae per acre as compared to untreated genotypes. Pyrethroid-treated Bollgard and Bollgard II cottons, along with untreated Bollgard II cotton, significantly lowered the numbers of bollworm-damaged bolls per acre below that of other treatment combinations. With regard to pupal and adult production per acre, both Bollgard and Bollgard II cottons in combination with either insecticide regime successfully reduced numbers of pupae and adults when compared to pyrethroid-treated and untreated conventional cotton. However, utilization of pyrethroid insecticides in addition to Bollgard II cottons may present the most effective resistance management strategy for bollworm in B.t. cottons.