The technique of treating sick people with magnets might not seem ripe for Food and Drug Administration approval, given that its most famed practitioner and advocate, Franz Mesmer, saw his claims demolished by a scientific panel that included Ben Franklin and Antoine Lavoisier.

Of course, technology has evolved since the time of Mesmer, the charlatan who mesmerized 18th-century Paris. Magnetic therapy might be returning, though perhaps the single most crucial discovery making this possible came only decades after Mesmer when Michael Faraday found that a changing magnetic field can spawn electric currents.

Now Neuronetics, a private company in Malvern, Pa., is awaiting the FDA's verdict on completed, peer-reviewed studies of its magnet-based, depression-treatment system, which builds on advances ranging from Faraday's Law to modern neuroimaging studies. It's a variant of a technology called repetitive transcranial magnetic stimulation (rTMS), approved for clinical use in many Western countries (though not the United States) and used in brain research for about two decades. Officials at Neuronetics say that the treatment might eventually serve to treat other illnesses, including schizophrenia.

A study in the June 13, 2007, issue of Biological Psychiatry shows that the system offers "a sustained benefit over six months with very low relapse" among some unusually tough depression cases, says Mark Demitrack, Neuronetics' chief medical officer. "We're basically coming to what we believe is the later stages of the FDA review." Neuronetics conducted the study with multiple partners that included the University of Pennsylvania.

In rTMS, electrical pulses sent through a coil create a fluctuating magnetic field. An electrical field duly appears around it, as Faraday noted, producing currents in any nearby conducting object, such as a brain. The basic technology isn't new, but Neuronetics claims to have helped transform it from an impractical, slow-acting research device to a sleek, powerful machine called the NeuroStar, suitable for doctors' offices.

For therapeutic uses "you're not talking about just one or two magnetic pulses, but thousands," Demitrack says. "That requires a different type of device."

Neuronetics officials credit Emory University neurologist Charles Epstein with originating the rTMS variant that became NeuroStar. Neuronetics licensed the technology and added refinements. A key change by Epstein was a simple, well-known trick of magnetism: Wrap the coil around iron, which then becomes magnetic itself and multiplies the field strength. If regulatory approval comes, he adds, Neuronetics' patented machine will be the only rTMS system to have obtained the agency's nod for therapy. He declined to reveal its cost.

The treatment involves stimulating the brain's left prefrontal cortex, as low activity in this area "is one of the most reliable, reproducible observations in major depression," Demitrack says. The system could either excite or suppress activity in other brain regions, depending on positioning and pulse frequency, he adds.

Neuronetics originated in 2003. As of late 2006 the company had raised $68.5 million in venture capital. Even old Ben Franklin might have been impressed.