While tens of thousands of tiny radio-frequency identification devices have been implanted in animals for years, there were suspicions that one day they would have use in humans, too. That suspicion was confirmed this week, when Mexico's Attorney General, Rafael Macedo de la Concha, reported that he had a chip implanted in his arm for security reasons.

Macedo went on to say that 160 of his employees had been implanted with the rice-grain-sized chips, manufactured by the VeriChip Corp.

Although developed and manufactured in the United States, the chips and the scanning technologies that work with them are still pretty much blocked for most human use in this country--although that could change if the FDA approves the devices for health care and medical use. VeriChip expects a decision from the FDA soon.

"We've sold about 7,000 [chips] worldwide," Angela Fulcher, VeriChip's VP of marketing and communications, said in an interview Thursday. "We think about 1,000 have been implanted in humans." Many final destinations of the chips aren't known, she said, simply because they are marketed through distributors, and VeriChip doesn't always know where they end up.

In addition, Fulcher suspects many are being tested in humans for military and governmental intelligence applications. "We can't talk about some applications," she said.

Fulcher points to potential markets for use of the RFID devices in humans. The security market surfaced for the first time publicly in Mexico City on Monday. At a cost of $150 a person, the chips were implanted in employees entering a new Mexican anti-crime information center in Mexico City.

Another application noted by Fulcher has similar security overtones: to use the chips as a secondary means of identification for credit-card users. She said VeriChip has been discussing that possible application with credit-card companies.

The application with the most potential for use in humans is in the health care field. An RFID chip implanted in a human can be read easily by a scanner and then referenced back to a central medical database. The unique ID--the company calls it the "VeriChip Subscriber Number"--is matched with the Global VeriChip Subscriber Registry. The password-protected data is maintained on two VeriChip database registry operations, one in Riverside, Calif., the other in Owings, Md.

The chips are implanted under a human's skin in a simple procedure. "Basically, it's like getting a shot," Fulcher said.

To date, the chief market has been in animals. Identifying cattle and other wildlife has been popular for years. For instance, salmon in the Northwest implanted with the chips are monitored by giant scanners located along river banks. The movement of cattle is monitored, too. And there's an emerging application for dogs and cats: an RFID device fitted with temperature-sensing capability can determine whether a pet is ill.