In the Côte d'Ivoire, since 1996, an increase of LD50 was recorded for deltamethrin and others pyrethroids in field populations of H. Armigera, one of the main pests observed on cotton. In the countries where bollworms have developped insecticide resistance, there are several mechanisms, from reduced penetration and nerve insensitivity to the metobolisation of the insecticide under the effect of monooxygenases or esterases. With the knowledge of the importance of metabolic resistance in H. Armigera, we decided first to determine if metabolic detoxification could be involved in H. Armigera pyrethroid resistance in Côte d'Ivoire