Kitty Hockman-Nicholas's phone is ringing off the hook. Callers to her dairy farm in Winchester, Va., are so eager to buy a share in one of her 20 hormone-free, grass-fed Jersey cows that she expects her 150 cow co-owners to double in number this year.

Why buy a cow? For the unpasteurized raw milk. A growing number of consumers are keen to drink raw milk, for reasons ranging from a desire to buy locally produced food to taste to a belief in its purported health benefits. Word of mouth abounds of how raw milk cleared up asthma and ear infections in children, improved osteoporosis in seniors, and even made autistic kids function better. (Pasteurization—subjecting milk to a short burst of heat to kill bacteria, followed by rapid cooling—has been standard protocol since the 1920s in this country.) Sally Fallon, founding president of the Weston A. Price Foundation, a Washington, D.C.-based advocate for consumption of whole, natural foods, estimates that more than 500,000 consumers regularly consume raw milk and claims that the number "is growing exponentially."

Accurate sales estimates are hard to come by, though, since the government is firmly opposed to raw milk and in many states—like Virginia—the only way to get some legally is to tap right into the cow. (U.S. News interviewed farmers at more than a dozen dairies from Virginia to California, and all reported a significant bump in sales of raw milk or in dairy cow ownership in the past few years.) Scientists warn that no evidence exists to back up most of the reported health benefits of raw milk and that there are serious risks of infection from listeria, salmonella, and E. coli. From 1998 to May 2005, raw milk or raw-milk products have been implicated in 45 foodborne illness outbreaks in the United States, accounting for more than 1,000 cases of illness, according to the Centers for Disease Control and Prevention. And that's probably an understatement, the report notes, since foodborne illnesses often go unrecognized and unreported.

"It's like playing Russian roulette with your health," says John Sheehan, director of the Food and Drug Adminstration's Division of Dairy and Egg Safety. The dangers, he says, range from mild food poisoning to life-threatening illness. "One complication that can arise as a result of infection with E. coli O157:H7 is hemolytic uremic syndrome, which can cause acute renal failure, especially in the very young or the elderly," Sheehan says. "There are absolutely no health benefits from consuming raw milk."

Indeed, it's only in the case of asthma and allergy that some evidence exists to suggest a possible protective effect. A study published in the June 2006 issue of the Journal of Allergy and Clinical Immunology by researchers at the University of London analyzed the diet of 4,767 children in Shropshire, England, and found that those who lived on farms and drank raw milk had significantly fewer symptoms of asthma, hay fever, and eczema. Children who drank raw milk were 40 percent less likely to develop eczema and 10 percent less likely to get hay fever than their peers who didn't drink raw milk. A second European study of nearly 15,000 children published in the May 2007 issue of Clinical and Experimental Allergy found that children who drank raw milk were less likely to have asthma and hay fever. Still, both reports warned that raw milk often harbors pathogens, and neither recommended consumption of raw milk as a preventative measure.

While there are no laws against drinking raw milk straight from the source, the government banned interstate sales more than two decades ago, leaving states to decide what to do when consumers within their borders want to buy raw milk. Twenty-three states ban the sale of raw milk for human consumption; the rest allow the purchase under certain conditions. In Maryland, a farmer who is caught selling raw milk runs the risk of jail. In California, raw dairy products are sold in some grocery stores. In Illinois, consumers can buy straight from the farm if they bring their own containers. In Virginia, it's legal to drink raw milk only from a cow that you own.

Raw-milk advocates like Fallon, who swears by raw milk for her own family, contend that pasteurization greatly reduces vitamin C and affects B6 and B-12 and beneficial bacteria such as lactobacillus. Sheehan does not argue with the fact that pasteurization destroys some vitamins and enzymes, but he calls the losses insignificant.

One possible alternative for aficionados of the local and natural: Drink very fresh milk from a well-run local dairy that doesn't practice homogenization (a process that breaks up and blends in the fat molecules to prevent cream from rising to the top) and uses a pasteurization process done at a relatively low temperature for a long time. "This method eliminates harmful bacteria with minimal impairment of flavor," says Anne Mendelson, a culinary historian and author of Milk: The Surprising Story of Milk Through the Ages.

Hockman-Nicholas, 67, has been drinking raw milk her entire life and says she has never been sick from it. Nor, she says, has she had a complaint from any of her customers, who pay about $80 up front and $28 per month for a cow share that produces 1 gallon of raw milk per week. Because she runs a grade A dairy, the top level for dairy farmers, the milk is tested frequently for quality by the state, and the facility is inspected regularly by the Virginia Department of Agriculture for the sanitation of the equipment and surroundings. The farm is also USDA-inspected. Hockman-Nicholas's cows are routinely tested for tuberculosis and brucellosis (they've never come up positive, she says). And bacteria levels in the milk are monitored.