Worried parents trying to get the lead out of their children's toy boxes have been taking matters into their own hands and buying home test kits.

The problem, according to the U.S. Consumer Products Safety Commission, is test kits commonly available are not reliable. "In a lot of cases, we're seeing these false negatives and false positives, and parents are panicking," said Ed Kang, a spokesman for the commission. Yesterday, the agency advised consumers against relying on consumer test kits.

Concern over the presence of lead in children's products has been heightened following a rash of recalls this year involving major toy makers such as Mattel and RC2 Corp. In the past week alone, 200,000 bookmarks, 55,000 Halloween pails and 5,400 children's puppet theaters were all found to have excess lead. Lead paint is toxic if ingested by young children.

This fall, the Consumer Products Safety Commission decided to do a special evaluation of consumer lead tests. The agency had done similar tests in the past but wanted to review the latest kits now being sold to shoppers. "The demand is certainly high," said Mr. Kang.

More than half of 104 tests done using the kits inaccurately indicated contaminated products were safe. Two test results came up positive when there wasn't any lead present.

"Based on the study, consumers should not use lead test kits to evaluate consumer products for potential lead hazards," the agency advised in an official statement yesterday.

According to the commission, its staff studied two common types of home test kits based on rhodizonate ion or sulfide ion. The agency said most of the kits were developed to detect high levels of lead in household paint, which means they don't work well detecting low levels of lead in paint or on other materials, such as metal jewelry. Also, both types of kits can be affected by dirt or paint colors that can make it hard to interpret the results.

The government agency did not identify the brands of kits that its staff reviewed but advised consumers that testing by a qualified laboratory and trained personnel was the only way to accurately assess risk.

If parents decide to try the kits and then feel the results warrant further checking, Mr. Kang said, they should consider sending items to a lab. "We're trying to just avoid panic when possible."

A list of laboratories is available on the commission's Web site, www.cpsc.gov/BUSINFO/testtoylabs.html. Consumers also can sign up for e-mail alerts on future recalls.

The next issue of Consumer Reports magazine is scheduled to include information on home lead testing kits.

In general, toy recalls are triggered by various sources. The commission may run tests after receiving numerous reports of problems or a toy manufacturer may discover an issue after doing its own tests.

After lead paint was discovered on more than one batch of toys this year, a number of manufacturers and retailers launched their own rounds of testing. Products made in China have come under particular scrutiny, in part because so many toys sold in the United States are made there.