Millions of genetically modified mosquitoes are being released into the wild in the Brazilian city of Juazeiro to try to wipe out dengue fever.
The viral disease affects between 50 and 100 million people a year.
While symptoms of the illness - which occurs in tropical climates - are usually mild, around 1 in 20 people will become seriously ill.
Currently, there is no vaccine and no treatment, so the only way to fight the disease is to destroy the mosquitoes that carry it.
Up until now, pesticides have been used to kill them, but they are becoming increasingly resistant.
This latest experiment means, if successful, the mosquitoes will be removed from the "cleansed" area and the dengue fever prevented from spreading.
The plan, reported in the New Scientist , is for the GM mosquitoes to mate with the natural mosquito to create offspring that die before reaching adulthood because of their infected genes.
That would make them incapable of spreading the disease.
If it works, the scheme could be used on other unwanted pests.
The method has already been used elsewhere, according to the report, having helped to eliminate the screwworm fly from the US and the tsetse fly - known for being linked to the deadly sleeping sickness - in Zanzibar.
Enthusiasts of the GM model say such an approach is effective because it focuses only on the species to be controlled, whereas pesticides harm other species in the chain, including humans.