Science has spoken when it comes to the theory that some childhood vaccines can cause autism. They don't, the Institute of Medicine concluded three years ago.

Soon, it will be the courts turn to speak.

More than 4,800 claims have been filed against the federal government during the past six years alleging that a child contracted autism as a result of a vaccine. The first test case from among those claims will be the subject of a hearing that was to begin Monday in a little-known "People's Court" - the U.S. Court of Federal Claims. A special master appointed by the court will hear the case.

For the parents filing a claim, there is the potential for vindication, and for financial redress.

The test case addresses the theory that the cause of autism is the measles, mumps and rubella vaccine in combination with other vaccines containing the preservative thimerosal. That preservative, which contains a form of mercury, is no longer in routine childhood vaccines. However, it is used in influenza vaccines.

One of the parents who has filed a claim against the federal government and has great interest in the case is Scott Bono of Durham, N.C. His son, Jackson, 18, has autism. While acknowledging the findings of the IOM's study, Bono believes those findings were preordained by the federal government.

"The charge before the IOM committee was: 'You're not going to find anything wrong here,"' Bono said.

He said that parents of children with autism have been marginalized, but they see specific outcomes in their children that are consistent with exposure to mercury. And those outcomes did not present themselves until after they received their vaccinations. In short, the children tell the story better than the numbers, he said.

"It's a thrill in the sense that, for the first time, the stories of these children are going to be heard in court," Bono said.

In July 1999, the U.S. government asked vaccine manufacturers to eliminate or reduce, as expeditiously as possible, the mercury content of their vaccines to avoid any possibility of infants who receive vaccines being exposed to more mercury than is recommended by federal guidelines.

Dr. Paul Offit, who developed a vaccine for the rotovirus, is chief of the division of infectious diseases at the Children's Hospital of Philadelphia. He said epidemiological studies pick up minute, almost invisible differences in the populations that have received a vaccine versus those that have not.

For example, a swine flu vaccine in the 1970s caused the sometimes paralyzing Guillain-Barre syndrome in one out of 100,000 cases, he said.

But no such correlations have been found for autism, which affects about one out of 150 children, he said.

"It should be easily picked up," he said. "It hasn't been and the reason it hasn't been is because vaccines do not cause autism."

Offit said mercury is part of the natural environment. There's no escaping it and, in fact, children will get more mercury from breast milk than they get from a vaccine. Yet, he's frustrated when he hears legislators speak of having zero tolerance for mercury.

"On this planet you can't have zero tolerance for mercury," he said. "You would have to move to another planet."

Autism is characterized by impaired social interaction. Those affected often have trouble communicating, and they exhibit unusual or severely limited activities and interests. Meanwhile, classic symptoms of mercury poisoning include anxiety, fatigue and abnormal irritation, as well as cognitive and motor dysfunction.

The report from the Institute of Medicine pointed to five large studies, here and abroad, that tracked thousands of children since 2001 and found no association between autism and vaccines containing the preservative thimerosal.

Members of the National Autism Association see drug manufacturers and the federal government as working too closely together to the point that the federal government is working to protect the industry from liability. The association says its mission is to raise awareness of environmental toxins as causing neurological damage that often results in an autism or related diagnosis.

Bono, a member of the association, said he doesn't believe his son was intentionally poisoned.

"I just want someone to step up and say, 'You're right, this did happen,"' he said.

During the hearing, lawyers for the parents were expected to present their expert testimony during the first week. Then lawyers representing the federal government were expected to present their case. The hearing was to be open to the public.

Officials planned to post transcripts on the court's website about 24 hours after each day's proceedings.