The ability to move bacterial genes encoding 'natural' insecticidal proteins into plants is permitting the development of crops intrinsically resistant to insect attack, with advantages over conventional insect-control agents (i.e. externally applied synthetic chemicals). These advantages include absence of residues in soil or groundwater, lack of toxicity to non-target organisms, and protection of plant parts which are difficult or impossible to spray (e.g. roots). Continued elucidation of the mechanisms by which such agents act, coupled with genetic engineering techniques, should lead to an increasing variety of insect-resistant crops in the coming years. Agriculture will thus gain inexpensive, effective and environmentally safe alternatives to current insect-control methods.