A memo from the drug maker Merck & Co. (search) shows that its executives were concerned about high levels of mercury in children's vaccinations nearly eight years before federal health officials disclosed the threat, the Los Angeles Times reported Tuesday.

Six-month-old children who received shots could get a mercury (search) dose up to 87 times higher than guidelines for the maximum daily consumption of mercury from fish, according to the March 1991 obtained by the Times.

"When viewed in this way, the mercury load appears rather large," Dr. Maurice R. Hilleman (search), an internationally renowned vaccinologist, wrote to the president of Merck's vaccine division.

The memo came at a time when health authorities were recommending shots for children that contained an anti-bacterial compound called thimerosal (search), the Times reported. Thimerosal contains mercury and was once used in the measles-mumps-rubella vaccine (search).

In 1999, federal health officials warned that routine vaccinations were exposing many infants to high quantities of mercury.

Merck officials declined to discuss the memo with the Times because of pending litigation.

Mercury-laced vaccines have led to more than 4,200 claims in a special federal tribunal by parents who claim their children were harmed as a result. Alleged injuries include autism (search) and other neurodevelopment disorders.

The newspaper obtained the memo from a lawyer who works with parent groups on vaccine safety issues and who said he acquired it from an unidentified whistle-blower.

Thimerosal has been largely removed from pediatric vaccines in recent years.

Separately, Merck faces hundreds of lawsuits over Vioxx (search), the popular painkiller it introduced in 1999 and pulled off the market in September.

The company, based in Whitehouse Station, N.J., has been accused in the suits of marketing a drug that caused heart problems and concealing the risks. Merck has denied the allegations.