The susceptibility to Bt toxins in Australian field populations of Helicoverpa armigera and Helicoverpa punctigera has been monitored at the Australian Cotton Research Institute since 1993 (Forrester and Bird 1996). This paper reviews the methods and results for the Bt resistance monitoring survey for the 1999/2000 cotton-season and compares them with data from previous seasons. No changes in susceptibility to discriminating doses of Dipel or MVP2 have been recorded in any of the Australian field populations of H. armigera or H. punctigera collected from cotton to date. Significant reductions in susceptibility to Dipel or MVP2 were recorded in field populations of H. armigera collected from sweet corn crops in coastal Victoria