Household pets can sometimes provide clues that children are suffering from lead poisoning, because they are more likely than humans to show severe symptoms, according to new research to be published in thie New England Journal of Medicine.

The researchers, Robert Dowsett of the University of Massachusetts Medical Center and Dr Michael Shannon of Children's Hospital in Boston, discovered three cases of lead poisoning in children in two different families after their pets became ill.None of the children showed signs of any illness, but tests uncovered high levels of lead in their blood.

In one case, cited by Dowsett and Shannon, a family dog that suffered from persistent vomiting and weight loss was treated for lead poisoning. Nine months after recovering, the dog's blood-lead levels rose again to 12 times the acceptable level.

The family's 1- and 3-year-old sons were then tested and found to have lead levels two to five times above the federal limit of 10 micrograms per deciliter of blood.

A microgram is 35 billionths of an ounce. A deciliter is about 3.5 ounces of blood.

The lead was found to have come from paint chips from the exterior of the house, which had been renovated months earlier.

The children and the dog had been eating the chips.

The second case was discovered after a pet cat suffering from vomiting, sleepiness and an unsteady gait was found to have lead poisoning. The family's 2-year-old child was found to have blood levels 2.4 times too high.

Lead is a silent disrupter of the brain. Long-term exposure can produce memory loss, abnormal behavior, coordination problems and headaches.