Has the introduction of Bt genes into the cotton plant affected its capacity for compensation after insect damage? This question is relevant for three reasons. First, and most obviously, Bt cottons remain vulnerable to non-Iepidopteran pests, including thrips and minds. Second, they are susceptible to Helicoverpa spp. when Bt efficacy drops because of crop ageing. Third, under some (yet undefined) environmental conditions, Bt efficacy can be low even in young crops, and we have seen fruit shedding in young commercial Bt crops that has been attributed to Helicoverpa damage. We assessed the degree of tolerance of Bt cotton to actual and simulated insect damage in three field experiments carried out at ACRl in 1996/97. Yield and maturity responses to damage of Bt cottons compared well with those of conventional varieties. The introduction of Bt genes into cotton does not seem to have reduced the considerable capacity of the crop to tolerate insect damage, and this attribute should be considered in the development of pest management strategies for Bt crops.