A good number of folks have started "chipping" their pets these days. That's when you have a tiny, encased computer chip inserted under the skin of your dog or cat. All sorts of information can be encoded on the chip, from the name of the animal's owner--useful in case the animal gets lost--to information about its medical history. A quick scan with the right device and this data comes popping up on a screen.

Other people are made uncomfortable by this technology. Leaving aside the issue of whether Big Brother will soon be watching Fido, a simpler question should be asked: is chipping your pet a safe thing to do? Not entirely, says a study in the journal Toxic Pathology, and it has nothing to do with privacy. The concern raised is that tissue under the skin can react to implants in negative ways, causing inflammation. In some animals, the reactions caused by having a chip can even lead to tumor formation.

Studies suggest that the culprit here is a gene called p53. Animals that have the p53 gene are more likely to develop tumors around chips, while those that don't are less likely. And in case you're planning to chip yourself, be aware that some people also have the p53 gene.

Still, about twenty-five million animals, from house pets to racehorses, have been chipped with no adverse effects. The benefits may well outweigh the dangers. But as with any new technology, pet owners--and people who think Big Fido may soon be watching--should be aware of the risks.