Domestic ferrets are the Harry Potters of the pet world. Like the popular book series, the furry, weasel-like mammals are a runaway hit with both kids and adults. With an estimated 6 million in homes across the country, their owners are passionate about them: forming clubs, organizing competitions and fighting for ferrets' rights--both political and medical.

Domestic ferrets (Mustela furo) are not rodents. They are intelligent, lively mammals--cousins to weasels and badgers--that have long, light bodies: males reach five to six pounds and females about one to three. They are playful and love to squirrel away small household items.(Furo means thief). They are relatively easy to care for--they can be trained to use a litter box--and they enjoy human companionship.

But concerns exist about ferrets' suitability as pets, especially in homes with small children. In July, a 2-month-old boy in Canada was reportedly attacked in his crib by his mother's ferret; the baby suffered 50 cuts to each foot plus several deep gashes around his face and eyes.

While many vets are loath to declare ferrets more dangerous than other pets, such incidents prompt experts to be cautious about endorsing them as family pets.

"If asked, my first response would be, 'Do you have babies?' " said Robert Ridgway, a veterinarian who serves on the board of the DC Academy of Veterinarians. "For somebody with children in cribs, ferrets are a no-no."

Some states--California and Hawaii among them--and some cities, including New York, have laws banning the animals as pets.

Bruce Williams, a veterinary pathologist at the Armed Forces Institute of Pathology in Washington and a ferret owner, believes ferrets don't deserve a bad reputation. "They make excellent pets, they are perfect for apartment dwellers," he said. "They don't need the space that a dog would. But they need people to spend time with them."

Still, Williams said, ferrets do not make ideal pets for everybody. "They are not for families with children under 6--I wouldn't recommend kittens or puppies to families with children under 6, either--or if they have them, they must be supervised. And plan to devote the same time as you would a dog."

"They are full of life," said Wanda Larkin of the Baltimore Ferret Club. "They are like having a 2-year-old child with four legs. They are cunning in a fun kind of way."

Larkin has three. She keeps hers in cages except during their playtime, which lasts two to three hours a day. Although she is retired and not very mobile, she said, her ferrets are easy to keep.

Larkin and her husband were shocked in 1989 when they moved from Virginia to Baltimore County, where they learned that ferrets were considered exotic animals, rather than domestic animals like dogs or cats. This meant "you could own [ferrets] but you couldn't buy or sell them," she said. So Larkin worked toward getting the animals reclassified as domestic, and also pushed to change the way that Maryland officials treat ferrets suspected of having rabies.

"It used to be that if you were scratched by a ferret, even if it had a rabies shot, animal control would seize the ferret" and destroy it to see if it had rabies and if the person needed to be immunized against the disease, Larkin said. But with a quarantine system now in place throughout Maryland, a ferret that has bitten someone is monitored for 10 days in a shelter or at the owner's home to ensure that it is disease-free.

Larkin said she still hears reports that Maryland ferrets are being put down over suspicion of rabies. The problem, according to a spokesman for Montgomery County Animal Control, is that Maryland only recently recognized the rabies vaccine used for ferrets.

With their popularity growing, the demand for veterinarians who specialize in ferret health has also increased. Ferrets require annual vaccinations against canine distemper and rabies, and should be checked for heartworm and have their teeth and stool examined.

As many as 25 percent of ferrets develop tumors on their adrenal glands, a condition called hyperadrenocorticism, characterized by a loss of body hair, increased aggression and, in females, an enlarged vulva.

"Every bald ferret is a ferret that you can help," said Williams, who describes hyperadrenocorticism and many other ferret illnesses and ways to treat them on his Web site (www.afip.org/ferrets).

The standard treatment is surgery to remove tumors, he said. But veterinarian Charles Weiss, a colleague of Williams's who specializes in ferrets at Potomac Animal Hospital in Potomac, has developed a new option which involves freezing the adrenal tumors instead of removing them. He plans to detail his findings at two veterinary conferences this January, which he hopes will encourage other vets to try it.

The standard surgery is technically difficult, especially when the tumor is on the right side, where it attaches to the vena cava, one of the main vessels circulating blood back to the heart. Instead, Weiss freezes the tumor with a probe, avoiding the danger associated with detaching it from a crucial artery.

The freezing method, called cryosurgery, also results in less bleeding and a shorter recovery. "Usually with normal surgery, within five to seven days they're feeling normal," said Weiss. "But with cryo, it takes only two to three days."

The standard adrenal-tumor surgery generally runs between $250 to $300 but could cost up to $1,000, said Weiss.