1. 
In 1998 GM maize contaminated organic maize in Texas.  This was discovered following the testing of organic tortilla chips, costing their producer (a small US company) US $150,000.

2.
In September 2000, GM Starlink Maize approved only for animal feed was found in food products meant for human consumption, such as taco chips. The causes were attributed to farmers failing to observe separation distances between GM Starlink maize and conventional maize, and the mixing of GM and conventional maize in post-harvest operations.  Allergenic reactions, many serious, were reported by at least 50 Americans. Food companies like Kraft, Safeway and Western Family spent millions of dollars recalling foods containing GM Starlink Maize. The cost to the biotech company that produced this maize, Aventis, was estimated at $1 billion.

3.
A soybean crop intended for human consumption was contaminated by a GM pharmaceutical maize crop (maize genetically modified to produce medicine) being grown by the biotech company, ProdiGene, to produce an experimental vaccine against a pig disease (Transmissible Gastroenteritis Virus or TGEV).  On November 12^th 2002, the United States Department of Agriculture (USDA) announced that it had quarantined half a million bushels of soybeans (worth over 42.7 million dollars) at a grain elevator in Nebraska after it was discovered that stalks from a GM Pharm maize crop were mixed with soybeans meant for human consumption. The GM Pharm maize had been grown in a field one year but had appeared again the following year as a ‘volunteer’ crop, which was then harvested with the new season’s soybean food crop. The USDA ordered the soya to be destroyed and fined the biotech company, ProdiGene $2.8 million dollars. The crisis caused the US government to tighten regulations on GM medicine crops, and prompted many scientists to call for medicine crops to be grown indoors, and in non-food crops.

4.
A study carried out by the Union of Concerned Scientists in the USA, published a report called “Gone to Seed” (2004), which examined the US seed supply to determine if seed stocks had been contaminated with GM material (DNA).  The research concluded that 50% of maize, 50% of soybean and 83% of oilseed rape seeds were contaminated with GM genes after only eight years of growing these GM crops in America.  The report warns that traditional seed supplies could be irreversibly damaged if this contamination which the report says is “endemic to the system” is not controlled.