Every night for the last year, Kathy Ruttenberg has been getting into bed with Trixie, a 7-kilogram Vietnamese pot-bellied pig.

"She's a great cuddler if you lie still," said Ms. Ruttenberg, a 53-year-old artist who lives near Woodstock, a rural community about 170 kilometers north of New York City. "But if you're restless, she gets annoyed, and her hooves are very sharp."

Figures vary, but according to a recent study published by the Centers for Disease Control and Prevention, 14 to 62 percent of the 165 million dogs and cats in the United States sleep in bed with their owners.

The reasons are well documented. First, touching, human or otherwise, raises levels of oxytocin in the body, creating feelings of contentment. And, of course, there is the comfort that an unconditionally loving animal provides in bed.

"Animals are uncomplicated and keep us in the present tense," said Mark Doty, the author of a memoir called "Dog Years," which chronicles the death of a lover. "When Wally could barely move, I saw him lifting his hand to reach over and pet Beau, our young retriever, who was curled up next to him."

It's no surprise that pet owners like Mr. Doty seem unconcerned about the study published recently by the C.D.C., in which two California doctors warn that allowing pets to sleep in the bed can be dangerous and can spread zoonoses, pathogens that go from animals to people.

According to Bruno B. Chomel, a professor at the University of California at Davis, and Ben Sun of the California Department of Public Health, the risks are rare, but real. They cite instances of fleas from cats transmitting bubonic plague. Cat scratch fever is a danger, they say, as are various forms of meningitis, Pasturella pneumonia and other infections.

But kicking pets out of bed isn't likely to be an option for many people. First of all, it's difficult to retrain animals once they have established a routine. Erica Lehrer and Richard Goldman of Houston learned that when they tried to keep their three cats out of the bedroom after installing an expensive black carpet. "They staged a protest: cried all night, pounded with their cat paws on the door," said Ms. Lehrer, 52, a writer.

At least their cats are indoor animals. That means there is less risk of having mice and other critters deposited in the bed. Which brings us to dogs. Could all that they walk through and bring into bed be a risk to health?

"I'd say, just wipe them down and you'll be fine," said Lucy O'Byrne, a veterinarian at the West Village Veterinary Hospital in Manhattan.

Dr. Chomel doesn't disagree. There is far more risk, he warned, with pet licks and kisses. If you have a wound or if your immune system is compromised, licking should be avoided. It's also not good for babies. And there have been cases of animals spreading resistant strains of staph infections and other diseases by licking cuts and wounds after surgery, so it's not recommended that pets be allowed in bed then.

On the other hand, what would Patricia Garcia-Gomez have done without a dog in bed after major surgery? Six months after falling in love with her boyfriend, but not his territorial Rhodesian ridgeback, Sylvie (who made it clear that she didn't like her turf being invaded by urinating in his apartment while staring into Ms. Garcia-Gomez's eyes), she was recuperating when the Great Dane-size dog surprised her by joining her in bed. It was a great comfort.

"She's been in bed with us since," said Ms. Garcia-Gomez.

Even if licking is risky, the risks might well be offset by the benefits, given the evidence suggesting that pets can increase longevity and boost the immune system.

Cesar Millan, the tough-minded dog trainer known for his TV series "The Dog Whisperer," agrees that sharing a bed with a dog is fine. But he believes the dog should be invited up each night, just to show it who's the real leader of the pack.

"Then choose the portion of the bed where the dog sleeps," he writes in his book "Cesar's Way." "Sweet dreams."

Sometimes, however, sweet dreams are not an option, as Tracy Rudd, an illustrator in Manhattan, has discovered. One man she dated years ago picked up her growling, nipping Chihuahua and tossed her out of the bedroom, later to find his clothes soaked in urine. When Ms. Rudd, 47, met her current husband, she said she knew he was the one because when he put his arm around her in bed during the night, causing her dog to growl and nip at him, he didn't seem to mind.

"He just said he respected her for defending her space," Ms. Rudd said.

As a result, the dog respected him and a lasting marriage was born.

The New York Times