The project objective was to contribute to production of Helicoverpa resistant cotton cultivars by identifying proteins capable of blocking insect digestion. Plants normally attempt to protect themselves from insect feeding by making protein inhibitors which block the action of essential digestive enzymes. Recent work has shown that insects are able to overcome the effects of these inhibitors by producing new enzymes that are less sensitive to the inhibitors. This project characterised the digestive proteinases of H. armigera and investigated the effects of different classes of proteinase inhibitors on the types proteinases produced by the insect larvae. The effects on insect growth and survival of combining multiple proteinase inhibitors were also determined.