Paul isn't going to let anything get in the way of golf. He plays almost every day, and at 79 he doesn't hold back on his swing. So when Paul's shoulder hurt, he listened to the advice of other golfers and tried magnets.

The current popularity of magnet therapy seems to have started on the golf course, and golf pro shops were about the only place to buy therapy magnets. Now you can find them in department stores and pharmacies everywhere. Worldwide, it is a billion-dollar business and, according to thousands of scientists and physicians, a billion-dollar waste of money by an achingly gullible public.

Paul bought a magnet therapy kit for $49.95. The shoulder pain disappeared, and his handicap dropped from 20 to 17. It could be because he's playing golf more regularly, he admits, but he thinks that the magnets probably had something to do with it. So does his wife. Since she began putting magnets in her shoes, she says she doesn't get as tired. Paul says he would recommend magnets for anyone.

But Paul admits that he hasn't always followed his own advice. When his knee hurt, he didn't try magnets. He went straight to his doctor.

Many friends his age have been diagnosed with osteoarthritis. That's serious. Not only will it mess up your golf game, but it's also not reversible. Fortunately, X-rays showed no sign of osteoarthritis, and the pain seemed to go away without any treatment.

Paul's knee healed by itself; his sore shoulder probably would have, too. Most of the things that afflict us get better by themselves. Our bodies have a very sophisticated repair kit for injury or disease: Bones knit, blood clots, the immune system seeks out infectious agents.

That can make it pretty difficult to tell whether the remedies we take actually help. Whatever we happen to be taking when we get better usually receives the credit.

Paul's doctor advised him that magnet therapy is not scientifically proven. Nor is it approved by the Food and Drug Administration.

"That didn't surprise me," Paul says with a snort. "Doctors always want to give you a pill. They think everything is internal. I don't know how magnets work, but they were using them in China thousands of years ago."

That's true, but the Chinese also were using powdered rhinoceros horn to restore virility. Unfortunately, they still do, with the result that the world is running out of rhinos.

By contrast, genuine medical advances extending and improving our lives today emerge from a detailed scientific understanding of how the body works. Viagra, for example, may yet save the rhino from extinction. The history of medicine is littered with the bones of traditional treatments that millions of people once swore by but now are known to be worthless or even harmful.

In The Fragile Species, Lewis Thomas notes that treatments such as purges and leeches were abandoned only when objectively compared to simply allowing the illness to take its course. Magnet therapy, it seems, has been abandoned many times over the centuries only to be revived [see box below].

So what has science learned about the effect of magnetic fields on the human body? Quite a lot, actually. Research has been driven not by magnetic therapy but by safety considerations associated with the phenomenal growth in use of magnetic resonance imaging (MRI) for medical diagnoses and research.

MRI subjects the whole body to a magnetic field about 100 times stronger than the localized field of a therapy magnet. Happily, no ill effects been found from exposure to MRI fields.

Indeed, there are almost no effects at all -- just a few faint sensory responses, such as a slight metallic taste and visual sensations of flashing lights if patients move their eyes too rapidly. The fact is that the stuff we're made of just isn't very magnetic.

That's why scientists were surprised two years ago when physician Carlos Vallbona at the Baylor College of Medicine in Houston reported results of a double-blind trial of magnets in treatment of 50 patients suffering post-polio pain.

Some of the patients were treated with commercial therapy magnets and others with sham magnets. After 45 minutes, 76 percent of those treated with real magnets reported a decrease in pain; only 19 percent receiving the placebo felt an improvement.

However, no confirming studies have been reported by other researchers. And in a published paper, Leonard Finegold, a biophysicist at Drexel University, criticized the protocol used in the Baylor trial.

The University of Virginia is finishing a two-year, double-blind study of devices sponsored by the National Institutes of Health's alternative medicine office, and results are to be announced soon.

Meanwhile, scientists might be more inclined to take the whole idea seriously if there were some plausible explanation of how the magnets work. Vallbona agrees that it's important to find a mechanism, saying he believes that magnets promote the flow of blood to the treated area.

One suggestion is that magnets attract blood because some blood cells contain iron. The iron in hemoglobin, however, is in a chemical state that is not ferromagnetic -- that is, not attracted to a magnet.

You can test this. An excess of blood appears as a flushing or reddening of the skin. Skin turns red under a hot water bottle because blood is being diverted to the heated area to serve as a coolant.

But you will discover that placing a magnet of any strength against your skin produces no reddening. In fact, blood is weakly diamagnetic -- at sufficiently high fields, it would be repelled by a magnet.

It has also been suggested that a magnetic field causes water molecules in the blood to align, somehow improving circulation. In fact, no alignment of water molecules is observed even at the huge field strength of MRI magnets. At the temperature of blood, water molecules jostle each other so violently that their orientation is entirely random. To align them, a magnetic field would have to be strong enough to overcome this thermal energy.

John Schenck of General Electric's R&D Laboratory, the leading authority on the effect of MRI fields on the body, calculates that fields thousands of times stronger than any ever generated on Earth would be needed to align a significant fraction of the water molecules.

The same is true of claims that the magnetic field separates positive and negative ions (electrically charged atoms) in flowing blood. The ability of magnetic fields to affect current flows in this way is known as the "Hall effect" and is a standard measurement of electron mobility in semiconductors such as the silicon in transistors.

Ions, however, are much heavier than electrons. In addition, blood flows so slowly compared to electron motion that, once again, any effect would be wiped out by the agitated motion of the hot blood.

Indeed, at the field strength of therapy magnets, it's difficult to imagine any mechanism that would overcome thermal effects.

How strong are the fields of therapy magnets? In a kit like the one Paul bought, the gold-plated neodymium alloy magnets are rated at 800 gauss, measured at the surface of the magnet. A gauss is a unit of magnetic field density named after Karl Friedrich Gauss, a 19th century German scientist.

That's not much compared to the 30,000-40,000 gauss electromagnets used in MRI, but it's a lot for a small permanent magnet.

Fifty years ago, permanent magnets had to be long to keep the poles from demagnetizing and usually were made in the shape of a horseshoe. Development of thin, powerful permanent magnets using rare-earth compounds and various iron-based chemicals is one of the unsung triumphs of modern materials science, making possible everything from miniature headphones to laptop computers.

It also triggered the magnet therapy fad. No one was going to show up on the golf course wearing horseshoe magnets.

In general, makers of therapy magnets warn against using them "around credit cards or during pregnancy." The instructions with Paul's kit, however, showed a magnet being worn on the wrist.

Your wrist normally passes within an inch or so of your pocket or purse, and 800 gauss is certainly enough to wipe out the magnetically coded information on the cards. Since people who make these magnets often are paid with credit cards, they presumably have an interest in seeing to it that your cards stay in good working order.

Could it be that they make therapy magnets the way refrigerator magnets are made? Since refrigerator magnets are meant only to hold phone messages and Dilbert cartoons, they are designed to have a very short range field. This is done by making them in the form of narrow strips of alternating north and south poles [see illustration above].

You can test this. Take two identical refrigerator magnets of the thin flexible kind, not the molded ceramic ones. Slide one across the other. You can feel a little tug each time the poles line up. Right at its surface, such a magnet may be quite strong, but a very short distance away, depending on the width of the strips, the north and south poles will effectively cancel [see illustration above].

Even for a conventional bar or horseshoe magnet, the field falls off rather quickly with distance. But in refrigerator magnets with alternating poles, it happens much, much faster.

The magnets in the kit were in little Velcro pouches to be attached to the injured area with blue velvet straps. They must look dashing in the fitness center. I removed two of the magnets and slid one across the other. I could feel them clicking into place: Like like refrigerator magnets, they were made with alternating poles.

To learn how quickly the field fell off, I stuck one of the magnets on a file cabinet. I could hardly pull it off with my fingers. I then inserted sheets of paper between the magnet and the cabinet until the magnet no longer could support itself.

Ten sheets! That's just one millimeter, about 1125th of an inch. The effective field of these magnets -- and of the kind used in the Baylor study -- would hardly reach through the skin, much less into muscles and joints.

As health fads go, magnet therapy may not seem like a big deal. Magnets generally cost less than a visit to the doctor and certainly do no harm. But magnet therapy can be dangerous if it leads people to forgo needed medical treatment.

Worse, its popularity in the absence of convincing evidence tends to reinforce a distorted view of how the world works, leaving people vulnerable to predatory quacks if they become seriously ill.

It's like trying to find your way around San Francisco with a map of New York. That could be dangerous for someone who is really sick -- or really lost.

Robert L. Park is professor of physics at the University of Maryland and author of the forthcoming book Voodoo Science (Oxford University Press).

Helene Grossman, a graduate student at the University of California at Berkeley, contributed to this report.

The Magnetizers

In the early 16th century, Paracelsus, the famous Swiss alchemist and physician, began using powdered lodestone in salves to promote healing. A naturally occurring magnetic mineral, lodestone can move iron without touching, suggesting great and mysterious power.

However, William Gilbert, physician to Queen Elizabeth I and father of the scientific study of magnetism, pointed out that the process of grinding the lodestone into powder destroyed the magnetism.

Nevertheless, magnetic cures were introduced into England a century later by Robert Fludd as a remedy for all disease, if properly applied. That included placing the patient in the "boreal position," with the head north and the feet south, during treatment.

By far the most famous magnetizer was Franz Mesmer (1734-1815), a German physician who carried the technique from Vienna to Paris in 1778 and soon became the rage of Parisian society. Dressed in colorful robes, he would seat patients in a circle around a vat of "magnetized water."

While Mesmer waved magnetic wands over them, the patients held iron rods protruding from the vat. Eventually, however, Mesmer discovered that it was just as effective if he left the magnets out and merely waved his hand. He called this "animal magnetism."

Benjamin Franklin, in Paris on a diplomatic assignment, suspected that Mesmer's patients did indeed benefit from the strange ritual because it kept them away from the bloodletting and purges of other Parisian physicians.

Those physicians bitterly resented Mesmer, an outsider who was attracting their most affluent patients. At the urging of the medical establishment, King Louis XVI appointed a royal commission to investigate. This remarkable group included Franklin, then one of the world's foremost authorities on electricity; Antoine Lavoisier, founder of modern chemistry; and Joseph Guillotine, the physician whose famous invention would one day remove the head of his friend Lavoisier.

The commissioners designed a series of ingenious tests in which some subjects were deceived into thinking that they were receiving Mesmer's treatment when they were not, while others received the treatment but were led to believe they had not. The results established beyond doubt that the effects were due solely to the placebo effect.

The commission report, never surpassed for clarity or reason, destroyed Mesmer's reputation in France, and he retired to Austria.

Nevertheless, magnetic therapy eventually crossed the Atlantic. Its most famous practitioner in the United States was Daniel Palmer, who in 1890 opened Palmer's School of Magnetic Cure in Davenport, Iowa. Like Mesmer, Palmer soon discovered that his patients recovered just as quickly if he omitted the magnets and merely "laid on hands."

Thus was founded "chiropractic therapy," and the school became Palmer's College of Chiropractic.

How remarkable, as we enter a new millennium with all that science has learned, that magnetizers should again be attracting a wide public following. But now there is no commission of Franklins and Lavoisiers to challenge their claims.

More than skin deep?

Not all materials can be magnetized. Most of the familiar ones that can fall into the category called "ferromagnetic," meaning that they act much the same way that iron does in the presence of magnetic fields.

In addition, moving charges such as household electric currents generate magnetic fields as long as the current is moving. If the fields are produced by alternating current, their north and south poles will reverse, typically at the rate of 60 times a second in the United States. Permanent or bar magnets keep the same polarity indefinitely.

Magnetic field strength is typically measured in units called gauss or tesla. One tesla, named for Croatian-American physicist Nicola Tesla (1856-1943), is equal to 10,000 gauss -- named for German mathematician and astronomer Karl Friedrich Gauss (1777-1855).

One gauss is a relatively low-strength field but still higher than most of the magnetic fields you encounter in everyday life, which often are measured in milligauss (thousandths of a gauss).

The field strength, of course, decreases drastically with distance from its source. In general, it falls off as least as fast as the square of the distance. That is, going twice as far from an object reduces the field strength by a factor of four. Often the drop-off is even faster. According to measurements by the U.S. Department of Energy, for example, the magnetic field inside a typical kitchen toaster is about 120 milligauss. Only four inches away, however, the field strength declines to 40 milligauss, and at a foot away it approaches zero.

That's why even if you live in a home that is only 50 feet from a very high current electric transmission line, the field you're exposed to while walking around inside rarely exceeds 2 milligauss.

At high strengths, fields are ordinarily measured in teslas. A really high quality bar or horseshoe magnet might have a maximum field strength of about .1 tesla (1,000 gauss). A research electromagnet used in laboratories would have a strength of about 1.5 tesla, and the superconducting magnets used in magnetic resonance imaging (MRI) equipment might hit 3 tesla.

CAPTION: Many therapeutic magnet ads leave the impression that a powerful field extends a considerable distance into the flesh. In fact, within 1116th of an inch of its surface, the field strength of even a very strong "refrigerator" magnet -- the sort typically used in magnet therapy -- drops to one-fourth of its maximum value.

Magnet Strengths in Gauss at 6 inches from

Typical therapeutic magnet: ???

Big-screen TV: .05

Earth's magnetic field at surface: .5

Hair dryer or electric

shaver: .7

Electric can opener: 1.5

MRI: 30,000