For more than a decade, families across the country have been warring with the medical establishment over their claims that routine childhood vaccines are responsible for the nation's apparent epidemic of autism. In an extraordinary proceeding that begins tomorrow, the battle will move from the ivory tower to the courts. Nearly 5,000 families will seek to convince a special vaccine court" in Washington that the vaccines can cause healthy and outgoing children to withdraw into uncommunicative, autistic shells -- even though a large body of evidence and expert opinion has found no link. The court has never heard a case of such magnitude. The shift from laboratory to courtroom means the outcome will hinge not on scientific standards of evidence but on a legal standard of plausibility. The decision could not only change the lives of thousands of American families but also have a profound effect on the decisions of parents around the world about whether to vaccinate their children. Advocates of the vaccine theory have argued that the increase in cases was triggered by a mercury-based preservative in vaccines that, they say, is toxic to children's brains. The law requires people claiming they were harmed by a vaccine to bring the case in the special court first, but if they lose, they can still file suit in civil courts. Scientific advocates for the vaccine-autism theory ... say fears about damaging public health programs have prompted scientists and the government to hide evidence of a problem. Many of the families believe that the medical establishment and the U.S. Centers for Disease Control and Prevention have conspired in a massive coverup.