A new study has found that farmers in China who grew genetically modified rice had higher crop yields, used fewer pesticides and, therefore, had fewer health complaints than farmers who grew regular varieties. The results of the study are the latest development in a continuing debate over the wisdom of growing genetically modified foods.

Experts say China developed genetically modified varieties of rice in the mid-1990s. The hybrid rice contains genes from a number of different varieties that are resistant to disease and pests.

Before selling the modified rice commercially, the Chinese government wanted to find out how well it performed. The modified rice has not been licensed for sale.

Carl Pray is an agriculture professor at Rutgers University in New Brunswick, New Jersey. Professor Pray said he and his colleagues began studying genetically modified crops in 1999 at the start of the controversy over the potential health and environmental risks of the technology.

"I had already been working in China with these colleagues of mine for five or six years already, at that time, on other issues with regard to science policy. And we said, 'Well, it is time we stop doing all this arguing, and we actually get some serious numbers from farmers about what that impact is,'" he said.

In a study published in the journal Science, researchers compared the modified rice, also called transgenic rice, to regular rice varieties in two areas of China in 2002 and again in 2003.

In one group, farmers devoted all or part of their fields to genetically modified rice strains. They made their own decisions about whether or not to use pesticides. The other group of farmers only planted non-transgenic rice.

The scientists found rice yields were up to nine percent higher among farmers using one genetically modified grain, compared to a conventional variety. The survey data also show that farmers using genetically modified rice applied less than one pesticide treatment per season, compared to farmers growing conventional rice, who applied pesticide almost four times per year.

Professor Pray said farmers who grew genetically modified crops reported no health complaints, such as headaches, nausea and skin irritation, compared to rice growers exposed to greater amounts of pesticides.

"And, so, I think that what we feel is that, based on the survey that we have done, and based on the evidence that is available to us, that these varieties can have important economic benefits in areas where these pests are a major problem," he said.

Christof Then, of Greenpeace Germany, says pesticides should be eliminated from the environment using a number of natural strategies, including crop rotation, in which farmers vary their crops from one season to the next to avoid particular pests.

But he said genetically engineered foods are not the way to go. Mr. Then says he does not know whether genetically modified crops are safe to eat.

"There were some experiments being done with mice, and the mice showed clearly some immune reactions to this kind of toxins that are produced in the rice. So, we think it should not be grown and it should not be consumed," he said.

Published surveys show that only four countries, including the United States, account for 99 percent of the world's transgenic crop production.

Even if governments deem genetically modified foods, like rice, to be healthy and environmentally safe, there is a strong public bias that will have to be overcome before modified foods become a global mealtime staple.