The federal government is warning consumers not to use those home testing kits to check their children's toys and other products for lead contamination.
A new round of tests found most of the time, they don't even work.
News of lead paint in toys and other products has boosted sales of the inexpensive test kits.
They are supposed to tell you if your child's toy is leadfree, but the Consumer Product Safety Commission says save your money.
CPSC spokeswoman Julie Vallese says, "We just don't think it's a good idea because of the unreliability of these tests."
In more than half the products they checked -- these tests found no hazard -- when in fact, lead was present.
The University of Rochester did a similar test on household dust.
Almost two thirds of the time the home tests failed.
University of Rochester spokewoman Katrina Korfmacher: "If you use the swab and it comes out negative you think, 'oh, we have no lead. That's no problem.' and you do no further checking. And that's exactly when you should do further testing."
Manufacturers call their tests "accurate" and "lab approved" but admit they're no substitute for a professional inspection.
Homesafe, which sells both, says: "Those work just fine for toys as long as you understand they only test the surface, not three millimeters under the surface."
Experts fear in testing every toy parents are missing the biggest threat: lead paint in their homes. The CPSC says if you think your child's been exposed have them tested because lead may affect brain development even at low levels.