One was a middle-aged man who refused to get into the shower. The other was a teenager who was afraid to get out.

The man, Leonard, a writer living outside Chicago, found himself completely unable to wash himself or brush his teeth. The teenager, Ross, growing up in a suburb of New York, had become so terrified of germs that he would regularly shower for seven hours. Each received a diagnosis of severe obsessive-compulsive disorder, or OCD, and for years neither felt comfortable enough to leave the house.

But leave they eventually did, traveling in desperation to a hospital in Rhode Island for an experimental brain operation in which four raisin-sized holes were burned deep in their brains.

Today, two years after surgery, Ross is 21 and in college. “;It saved my life,”; he said. “;I really believe that.”;

The same cannot be said for Leonard, 67, who had surgery in 1995. “;There was no change at all,”; he said. “;I still don't leave the house.”;

Both men asked that their last names not be used to protect their privacy.

The great promise of neuroscience at the end of the last century was that it would revolutionize the treatment of psychiatric problems. But the first real application of advanced brain science is not novel at all. It is a precise, sophisticated version of an old and controversial approach: psychosurgery, in which doctors operate directly on the brain.

In the last decade or so, more than 500 people have undergone brain surgery for problems like depression, anxiety, Tourette's syndrome, even obesity, most as a part of medical studies. The results have been encouraging, and this year, for the first time since frontal lobotomy fell into disrepute in the 1950s, the Food and Drug Administration approved one of the surgical techniques for some cases of OCD.

While no more than a few thousand people are impaired enough to meet the strict criteria for the surgery right now, millions more suffering from an array of severe conditions, from depression to obesity, could seek such operations as the techniques become less experimental.

But with that hope comes risk. For all the progress that has been made, some psychiatrists and medical ethicists say, doctors still do not know much about the circuits they are tampering with, and the results are unpredictable: some people improve, others feel little or nothing, and an unlucky few actually get worse. In this country, at least one patient was left unable to feed or care for herself after botched surgery.

Moreover, demand for the operations is so high that it could tempt less experienced surgeons to offer them, without the oversight or support of research institutions.

And if the operations are oversold as a kind of all-purpose cure for emotional problems — which they are not, doctors say — then the great promise could quickly feel like a betrayal.

“;We have this idea — it's almost a fetish — that progress is its own justification, that if something is promising, then how can we not rush to relieve suffering?”; said Paul Root Wolpe, a medical ethicist at Emory University.

It was not so long ago, he noted, that doctors considered the frontal lobotomy a major advance — only to learn that the operation left thousands of patients with irreversible brain damage. Many promising medical ideas have run aground, Wolpe added, “;and that's why we have to move very cautiously.”;

Dr. Darin D. Dougherty, director of the division of neurotherapeutics at Massachusetts General Hospital and an associate professor of psychiatry at Harvard, put it more bluntly. Given the history of failed techniques, like frontal lobotomy, he said, “;If this effort somehow goes wrong, it'll shut down this approach for another hundred years.”;