The worst of those fears seemed to come true last year when a variety of biotech corn known as StarLink was found in taco shells made by Kraft Foods and sold in grocery stores throughout the nation.

The corn, genetically engineered with a pesticide protein to kill the European corn borer, was found in food even though the variety had not been approved for human consumption.

The discovery led to the recall of more than 300 products, and chaos among many farmers, grain distributors and food makers.

The U.S. Environmental Protection Agency has not yet ruled whether the biotech corn, made by Aventis CropScience of North Carolina, contains an allergen protein.

A panel of scientific advisers for the EPA have said that there is a "medium likelihood" that the pesticide protein in the corn could cause allergies in susceptible people. But new data indicate that only tiny amounts of the protein, known as Cry9C, are left in food after processing, probably far too little to cause allergies, said Steve Taylor, a food scientist and allergy expert at the University of Nebraska at Lincoln.

After StarLink was found in Taco Bell brand taco shells, hundreds of people stepped forward to say they had allergic reactions to the corn. The Food and Drug Administration is now testing blood samples collected from 18 of those people to see whether they have allergy antibodies to the Cry9C protein.

Aventis supplied the agency blood samples drawn from Red Cross donors before StarLink was introduced, blood from one person with a corn allergy and other samples from people who were allergic to nuts, a company representative said.

Even before the FDA has released any information about its testing procedure or the results of the blood tests, critics are contending that the agency's methods may be flawed. The type of test the agency has developed often gives falsely positive results, Taylor said.

If the FDA does find people who test positive for Cry9C allergies, the blood test will have to be followed with blind taste tests to confirm the result, an Aventis official said.

Many alternate explanations may account for reactions, said Bruce M. Chassy, a biochemist and food safety specialist at the Biotechnology Center at the University of Illinois at Urbana- Champaign.

Antibodies directed at other proteins may cross-react with the StarLink protein, or an unknown source of Cry9C in the diet may have made people sensitive to the protein. Those explanations are more likely to account for StarLink-related allergies than any contaminated foods, Chassy said.

"The least likely (explanation) is that somebody got sick from eating Taco Bell taco shells," he said.

The FDA should open its tests to independent labs for scrutiny and use more accurate tests to analyze the blood samples, Chassy said.