Taking into account the protection of natural environment, it may be expected that the use of Bacillus thuringiensis toxins to control pest insects will be increased. It results from the discovery of novel toxins with different activity spectra and from the creation of more active toxins with the use of genetic engeeniering techniques. Besides, the introduction of transgenic plants such as cotton, potato, tomato, tobacco and others producing the bacterial toxins against more important species of pest insects will significantly reduce the application of chemical insecticides. The possibility of resistance development in insects poses a great threat to the above strategy. The better recognition of biochemical, physiological and genetical mechanisms of resistance to B. thuringiensis toxins will allow to devise a strategy for delaying jnsects resistance. The general principles of this strategy are similar to those used in the case of chemical insecticides and involve the rational application of B. thuringiensis toxins and their rotation with other insecticides.