Health regulators in the United States are talked about as the best in the world, but a new study on the spread of stem cell clinics shows what can happen when regulations fall behind.

Out of nowhere, over the past two to three years, the clinics have sprung up — 570 in the United States, according to a recent paper — offering untested stem cell treatments for just about every medical use imaginable.

In theory, stem cells might be a useful treatment for certain diseases that involve the loss of cells, like Type 1 diabetes, Parkinson’s or osteoarthritis. They are primitive cells that can develop into a range of mature cells and perhaps serve as replacements. But progress is slow. After a flurry of stem cell excitement two decades ago, almost all the research today is still in mice or petri dishes. The very few clinical trials that have begun are still in the earliest phase.

An orthopedic clinic, for example, says on its website, “Stem cells actually restore degenerated tissue while providing pain relief.” Another clinic seeks patients with neurological diseases, asserting, “The regenerative nature of the fatty adult stem cells that are extracted from the patient can help improve the degeneration and ease the symptoms associated with the disease.”

The rapid proliferation of stem cell clinics “looks like it is occurring on a nationwide industrial scale,” said Leigh Turner, a bioethicist at the University of Minnesota, who, with Paul S. Knoepfler, a stem cell researcher at the School of Medicine of the University of California, Davis, published the new paper tallying the clinics. “It’s operating brazenly, out in the open. It leaps out of these cultural assumptions about hopes and dreams of stem cell treatment, but there is no science behind it.”

The Food and Drug Administration allows clinics to inject patients with their own stem cells as long as the cells, or the tissue the cells are extracted from, meet specific criteria, including “minimal manipulation,” and are intended to perform their normal basic function.

But even if treatments the clinics advertise seem questionable, the F.D.A. cannot act based on a website. “They have to have actual cases of clinics administering the cells to patients,” said Ubaka Ogbogu, an assistant professor of law at the University of Alberta in Canada who has studied the clinics and their regulation. “These clinics are being run by very sophisticated people. They understand the laws very well and have been working around the laws.”

Some clinics advertise treatments that seem to flout the regulations, offering, for example, stem cells from amniotic fluid, which do not qualify under the F.D.A.’s rules because they are not from the patient’s body. Others advertise stem cells collected from a person’s blood or fat to treat a neurological disease like Parkinson’s disease or multiple sclerosis. Those cells do not qualify because they do not normally function in the brain to control movement. There is no registry of patients going to these clinics, so it is unclear how many have been treated.

Outraged, Dr. Knoepfler has confronted some of the clinics.

“I have spoken to the clinics and they say, ‘O.K., you have lectured me about F.D.A. regulations, but I have been doing this for years and never heard a peep from the F.D.A.’ They see it as a tacit green light,” Dr. Knoepfler said.