A test case in an American court could in one way or another settle the debate on the possible link between autism and childhood vaccines.
In an unprecedented legal challenge in a special court in Washington, the Court of Federal Claims, the case of a girl from Arizona, is the first to be heard of more than 4,800 cases.
The cases have been filed by parents who believe their children's autism was caused by a mercury preservative in the vaccines.
Michelle Cedillo, a 12-year-old, suffers from a plethora of health problems, including severe autism, inflammatory bowel disease, glaucoma and epilepsy which her parents believe are the result of the MMR vaccine she was given at 15 months.
The parents want compensation from the National Vaccine Injury Compensation Program, a no-fault system with a $2.5 billion fund made up from a 75-cent-per-dose tax on vaccines.
This first test case will question whether the combination measles, mumps and rubella (MMR) vaccine, plus a mercury-containing preservative called thimerosal, caused Michelle's autism.
As vaccine experts point out parents often link vaccines with their children's symptoms because vaccinations can be upsetting, and children are vaccinated at an age when autism and related disorders often first appear.
A solid body of scientific evidence challenges the parents cases and medical experts and the Government have repeatedly assured parents that the MMR vaccine is safe.
According to the World Health Organisation a 95 per cent vaccination coverage of children is necessary to achieve "herd" immunity, where sufficient numbers are protected to prevent outbreaks and epidemics of disease.
But controversial research by Dr. Andrew Wakefield published in The Lancet in 1998, linking the MMR vaccine with autism and bowel diseases has fuelled the cause and public confidence appears to have been affected.