A series of field and laboratory tests evaluated the insecticidal and yield performance of selected transgenic cotton lines (BTK) from Delta Land and Pine Company, Cotton Seed International, and Stoneville Pedigreed Seed Company during 1997 in Louisiana containing the delta endotoxin of Bacillus thuringiensis kurstaki. All BTK cotton lines controlled the bollworm (BW), Helicoverpa zea (Boddie), and tobacco budworm (TBW), Heliothis virescens (F.), complex similar to that of the BTK standard cultivars, Coker 312-531 and NuCOTN 35B. All BTK lines also produced seedcotton or lint yields > to that of the BTK standards in both non-sprayed and sprayed treatment regimes. In the laboratory studies, BW and TBW mortality on squares of BTK cotton lines ranged from 48.8 to 97.5% and 75.4 to 97.5%, respectively, and were not significantly different from that of Coker 312-531. Also in the laboratory, no significant difference was observed between a transgenic BTK cotton (NuCOTN 33B) and the non-BTK cotton cultivar (DP 5415) in the number of squares injured by L1 stage BW. Although the number of squares injured by L1 and L2 stage TBW was significantly lower for NuCOTN 33B than for DP 5415, both stages injured >11% of the squares in the study.