WASHINGTON (AP) -- Families claiming that a mercury-based preservative in vaccines triggers autism will challenge mainstream medicine as they take their case to a federal court.

Two 10-year-old boys from Portland, Oregon, will serve as test cases that determine whether the children and their families in similar situations should be compensated from a government fund that helps people injured by shots.

Attorneys for the boys will attempt to show the children were developing normally until they were exposed to vaccines with thimerosal.

Thimerosal has been removed in recent years from standard childhood vaccines. Experts say there's no credible evidence that vaccines containing thimerosal caused autism, a developmental disability that typically appears during the first three years of life.

Overall, nearly 4,900 families have filed claims alleging that vaccines caused autism and other neurological problems in their children.

Copyright 2008 by The Associated Press. All Rights Reserved.