Families claiming that a widely-used fungicide left their children blind from birth are to learn whether they can sue its maker in US courts.
The UK parents say exposure to DuPont's Benlate in pregnancy caused babies to be born with no eyes.
The company, which denies the crop spray is to blame, has already had to pay out millions to one blind teenager.
A ruling - possibly late on Tuesday - will determine whether the six UK cases will be heard by an American jury.
Before its withdrawal in 1997, Benlate was used on tens of thousands of acres of agricultural land in the UK each year, and was one of the top selling agricultural products for DuPont.
However, tests in rats as long ago as the 1970s suggested that, at higher doses, the rate of birth defects soared.
Some scientists believe that, for just a few days early in pregnancy, at the time that the eyes form in a human foetus, exposure to benomyl, the principal ingredient of the spray, could disrupt their formation.
This might, in some individuals, cause a condition called microphthalmia, in which the eyes are much smaller than normally, causing seriously impaired vision - or even anophthalmia, in which the baby is born with the eyes completely absent and eyelids sealed shut.
In the 1970s, the US Environmental Protection Agency, on the basis of animal experiments, pushed for warnings on larger containers warning against exposure during pregnancy.
This was backed up by further research by the University of California in 1991.
But after lobbying from DuPont, which challenged the validity of the experiments, the recommendation was dropped.
However, the issue reemerged in the 1990s when a Florida couple successfully sued DuPont and were awarded more than $4 million after a Miami court decided that Benlate was responsible for their son being born without eyes.
Following this, UK families who felt there was strong evidence that Benlate could be linked to anophthalmia or microphthalmia in their children joined together to take DuPont to court, using the same law firm.
On Tuesday, a judge could rule whether the scientific evidence they intend to present in the case is admissible in court, potentially giving the green light for it to be put to a jury in a full hearing next year.
DuPont has always firmly denied that a link between Benlate and birth defects has been established by scientists.