Transgenic Bt cotton cultivars have been tested for 4 years in small plot replicated experiments and larger plot on farm replicated studies to determine efficacy against susceptible cotton pests. Results of this research project showed that transgenic Bt cotton provided excellent control of bollworm and tobacco budworm infestations. Transgenic Bt cotton was highly effective in cabbage looper control and showed significant suppression of beet armyworm. The transgenic Bt cotton cultivars tested showed no greater attractancy for or more susceptibility to tarnished plant bug or cotton aphid than other comparable non-Bt cultivars. Transgenic Bt cotton showed, in some cases, higher square set than other adapted varieties protected with insecticides.