In 1996 the Australian cotton industry introduced Ingard^® which expresses the Bt toxin Cry1Ac. Ingard^® has proved effective in controlling the Lepidopteran pest species Helicoverpa armigera and H. punctigera. Although laboratory selection produced a Cry1Ac resistant strain of H. armigera, genes conferring resistance to this toxin remain rare in field populations. In 2004/05 Bollgard II^® (which expresses both Cry1Ac and Cry2Ab) replaced Ingard^® in Australia, and now comprises 80% of the 250,000ha planted to cotton. The focus for resistance management has now shifted to Cry2Ab resistance, particularly in H. armigera which has a history of evolving resistance to conventional insecticides. In 2002 we began to conduct F₂ screens of field populations of this species to investigate the frequency of alleles that confer resistance to Cry2Ab. Such alleles proved to be more common than expected and characteristics of the first one detected (designated SP15) will be reported herein. Our current best estimate for its frequency in the field is 0.004. We will discuss the genetics, resistance levels, cross resistance, and fitness costs associated with Cry2Ab resistance in SP15, and the relevance of these findings to managing Bollgard II^®.