The recently planted rows of pineapple plants in the four-acre field on one side of the Malayon family home look neat and well-tended, but are otherwise not really worth a second glance.

But what occurred last year on and around this plot in Kalyong village, on the southern Philippine island of Mindanao, is threatening to turn this unremarkable field into a battleground in the war over genetically modified crops.

For the first time there are indications that the pollen from the bacillus thuringiensis (Bt) maize sown here last year may have contributed to human illness.

Terje Traavik, the scientific director of the Norwegian Institute of Gene Ecology, who was asked last October to analyse blood samples from 39 of the 100 people who fell ill, has said that a link might exist between GM crops and human health.

"My interpretation is there is a coincidence in time between two different phenomena," he said. However, he stressed that more tests were needed before a definite conclusion could be drawn.

The landowners, government officials, and Monsanto, the multinational company that provided the seeds planted on the plot, insist the corn is not the cause. They claim the villagers are being manipulated by anti-GM campaigners.

Villagers say the trouble began in July last year when the maize plants started flowering.

"There was this really pungent smell that got into our throats," said Maryjane Malayon. "It was like we were breathing in pesticides."

Her sister, Amaniel, their parents, Samuel and Merlina, and Maryjane's nine-month-old daughter, Eileen, began coughing, vomiting, feeling dizzy and suffering from head and stomach aches.

Within days people living a little further away, on the other side of the dusty road that runs through this village on the slopes of the remote 7,500ft (2,286m) volcano Mount Matutum, were experiencing similar symptoms.

Pablo Semon, a community leader, says about 100 people were affected.

Maryjane says the situation got so bad that the family was forced to move to a relative's home three miles down the mountain.

"We were the only ones who moved because we were so close," she explains. "But within a week we had all recovered."

A villager who had no home at the time, Bernhard Nanquil, says he rented the Malayon home after they left.

"Within a week I too was sick with a stomach ache and diarrhoea." Others noticed that their livestock was suffering.

"One day the horse ate some of the corn plants and its appetite disappeared," said Nestor Catoran. "The belly swelled, its mouth started frothing and it slowly died."

Villagers are linking the corn to the deaths of four other horses, which were disposed of without any analysis.

However, all the villagers are convinced that the corn is in some way responsible for their illness.

One of the owners of the land, Sensie Victoriano, accepts that the villagers fell ill, but laughs at suggestions it was because of the corn, tens of thousands of acres of which were cultivated across the country last year with no resulting accusations.

Ms Victoriano blames "a group of activists who are against GMOs".

Dr Traavik, who describes himself as a GMO sceptic and not an opponent, says it is highly unlikely the Bt toxin was the only cause of the villagers' sickness.

"There's no illness that's caused by only one factor," he said. "What happened in there [Kalyong] could have been an underlying viral infection that could explain the symptoms, but that does not exclude the possibility that this has been exacerbated by a new allergenic protein from the Bt corn."

The head of the corn programme at the department of agriculture, Artemio Salazar, has no time for the villagers' allegations.

"The phenomenon - the supposedly allergenic reaction - was also occurring in areas where there was no Bt corn," he said yesterday, without being able to name any of the other regions.

One of his microbiology experts, Nina Barzaga, from the University of the Philippines, added: "We have to see the results.

"But I think they're trying to create some panic ... the Bt toxin has never been associated with any sickness anywhere in the world."

Dr Traavik said he would be willing to share his results with Dr Barzaga but cautioned against saying there had never been problems with Bt maize.

Monsanto was not available for comment yesterday but said last week that it was extremely unlikely that the maize was responsible for ill health in the village.

"There have been no documented cases of allergic reactions to Bt maize after seven years of broad commercial use on millions of hectares in the US, Canada, Argentina, Spain and South Africa, starting in 1996," a spokesman told Reuters.