WASHINGTON Grace Booth had just finished a chicken enchilada lunch with co-workers when she began to feel hot and itchy. Her lips began to swell, she developed severe diarrhea and soon she was having trouble breathing.  Her colleagues called an ambulance. .

Ms. Booth, 35, was rushed from the California youth center where she works to a nearby hospital, apparently suffering from anaphylactic shock.  Doctors quickly injected her with anti-allergy medicine, gave her some Benadryl to swallow and put her on an intravenous injection mechanism. The treatment worked, and after five hours she walked out of the hospital. .

Several days later, Ms. Booth learned that taco shells and other corn products had been recalled nationwide because they were found to contain a genetically modified type of corn called StarLink. The corn had been approved for only animal consumption because of concerns it might trigger dangerous allergic reactions in people. .

Because there was corn in the tortillas Ms. Booth had eaten - and because tests for all other food allergies had been negative- she contacted the  Food and Drug Administration and reported that she might have had an allergic reaction to StarLink. Ms. Booth is among several dozen people nationwide  who believe they suffered allergic reactions from eating StarLink corn last fall. Their cases are being investigated by the FDA and the federal  Centers for Disease Control and Prevention. The outcome of that investigation  could have enormous ramifications for the future of biotech food. .

Allergic reactions have been viewed for years as the primary threat to  human health posed by genetically engineered foods, which typically have  proteins from other organisms spliced into them for various reasons. But the health complaints about StarLink are the first lodged by consumers against an engineered food. .

If researchers determine the unsuspecting persons did indeed have allergic reactions to a protein in the corn, then the already troubled world of agricultural biotechnology will suffer another damaging blow. Despite widespread concern over a possibility that genetically engineered crops could damage the environment or cause human health problems, there has  been little evidence that either has occurred. Allergic responses to StarLink would mark the first documented instances of people suffering health problems because of engineered food. .

But if the results come back negative, the industry will regain some credibility. Company scientists have argued that StarLink could not cause severe, or even minor, allergic reactions, and that the corn is safe.  That's why they say it should have been approved also for human use (rather than just as animal feed) several years ago. .

It has taken months for the FDA to develop a test for that potential allergic reaction, but officials say they believe they have one. It has  not been fully checked and double-checked, and researchers warn the test will not give a definitive answer. .

But officials said they are far enough along to seek blood samples from people like Ms. Booth, collected last year by the Centers for Disease Control and Prevention. The samples were scheduled to arrive in Washington last week, and testing is expected to begin this month. .

Karl Klontz, a medical officer with the FDA's Center for Food Safety and Applied Nutrition, said the test would determine whether the people had produced antibodies to the genetically modified protein in StarLink corn, called Cry9C, which protects plants against the European corn borer. .

"This is the first time a test like this has been developed, and nobody is claiming that it is a gold standard," Mr. Klontz said. "But the presence  of the antibody”š would suggest the possibility of an allergic phenomenon, and the lack of the antibody”š would go a long way to reassure that there is no allergic issue." .

If the antibody to Cry9C is found in the blood samples, he said, then skin-prick tests and even "food challenges" - the feeding of food  containing StarLink to possible allergy sufferers - could follow. .

Regulators have been especially concerned about engineering foreign  proteins into food because consumers have no way of knowing they might be present. People allergic to peanuts learn to avoid certain products, but  genetically engineered proteins are not labeled and so can't be easily avoided. .

The issue surfaced in 1995, when researchers found that a Brazil nut gene introduced into a soybean could cause allergic reactions. The problem was discovered before the soybean went to market, and research on the seeds  was stopped. .

StarLink corn was supposed to be kept from human food, but all involved acknowledge the system for doing that didn't work. .

The corn was discovered last fall to have been inadvertently mixed with  corn destined for the human food supply, prompting a massive and costly recall of corn and foods made with corn, including tacos, beer and, most recently, corn dogs. But since the recalls began, federal and industry officials  have emphasized that no significant health hazard was involved. .

In fact, in November, Aventis CropScience, which makes the corn, again  asked the Environmental Protection Agency to approve StarLink for human consumption, pointing to new research it said showed there was no risk of allergic reactions. Aventis had returned its license to sell the corn in  the future but wanted the variety approved for past seasons to limit  disruptions in the corn market - and, some contend, its own financial liability. .

The company argued then that the quantities of StarLink in processed food are too small to cause allergic reactions and that its research showed  that the Cry9C protein was destroyed in producing food such as tacos. The Cry9C found in tests of tacos was from cell DNA rather than actual protein, the company said, and so could not cause an allergic reaction. .

An EPA expert panel concluded several weeks later that there was a "medium likelihood" StarLink protein could cause an allergic reaction but that  there was a "low probability" that people had developed the needed sensitivity because of the limited amount of the corn in the food supply. However, the panel recommended that the EPA not act on the Aventis request until a test was created and used to evaluate reports of allergic reactions to  StarLink. .

The drug agency has received 48 such reports, and the Centers for Disease Control and Prevention has focused on the 35 that came in before the November advisory committee meeting. At that time, the FDA said about a dozen of the complaints appeared to involve allergic reactions. .

StarLink is suspected of causing allergies because Cry9C has a heightened ability to resist heat and gastric juices - giving more time for the body to overreact. The molecular weight of the protein is also consistent with something that can trigger an allergic reaction, the panel said.