To the editor:

Richard Gilmore's article in the December issue entitled 'US food safety under siege?' (Nat. Biotechnol. 22, 1503–1505, 2004) rightly points out the vulnerability of US agriculture to terrorist attack. The production, through genetic modification, of pathogen-resistant crops and animals is one of Gilmore's recommended counterattacks to the diseases and pathogens that might be used against us.

It might be productive for the biotech industry to first consider how genetically modified crops themselves could contribute to terrorist attacks. Just a few bushels of 'pharmcorn' producing a swine vaccine could, if strategically planted by terrorists, contaminate virtually the entire US corn supply and close international markets to us for years. Such crops are being planted in open fields throughout the United States, without fences or guards of any kind. The USDA's policy of not publicly revealing pharmaceutical crop locations other than by county is supposed to keep such crops out of the wrong hands. However, it is hard to imagine that relatively small fields requiring specialized equipment and multiple USDA inspections would not be readily recognizable to someone looking for them.

It would seem that before genetically modifying all of our crops and animals, there are simpler and more obvious steps that should be taken to protect the food supply.