Thimerosal, a preservative containing ethyl mercury used in some vaccines, should not be considered a harmful source of mercury or be subjected to a ban contained in the United Nations' draft treaty, the American Academy of Pediatrics said. Dr. Walter Orenstein of the AAP Committee on Infectious Diseases said reducing mercury exposure is important, but the use of thimerosal in vaccines is an exception because it is key to protecting children. The policy statement, published in the journal Pediatrics, supports WHO's stance on the use of thimerosal.