Skeptics once dismissed chronic fatigue syndrome (CFS) as a bizarre form of hypochondria among stressed-out young professionals. The illness, which was not even given a clinical name until 1988, was disparaged as "yuppie flu," and the profound weariness and mental disorientation suffered by its victims were often misdiagnosed as signs of depression. Now CFS sufferers have a persuasive ally. Last November, after gathering data on CFS for 18 months, the Centers for Disease Control in Atlanta gave an official stamp of legitimacy to the syndrome when they launched a new $1 million study to determine a possible cause. The leading hypothesis: a malfunction of the immune system.

Paul Cheney, 43, the doctor who with his then partner, Dr. Daniel Peterson, first brought the disease to the attention of the public 6½ years ago, believes the CDC study is long overdue. Cheney encountered his first cases of CFS in 1984 while working as an internist in the ski resort town of Incline Village, Nev. When local high school teachers came down with what appeared to be an extremely bad flu, Cheney prescribed the all-purpose remedy: rest. It didn't help. Within months, in fact, 173 similarly persistent cases emerged out of the town's 20,000 people.

Since then, Cheney, now in private practice in Charlotte, N.C, has examined more than 2,000 patients with the disease: he estimates that nationwide, CFS could afflict millions of people of all ages and walks of life. It became closely associated with yuppies, Cheney says, for the simple reason that they have been its most vocal victims. Cheney, who lives outside Charlotte with his wife, Jean, 43, a high school English teacher, and their two children, spoke recently about CFS with correspondent Sarah Skolnik.

What are the symptoms of CFS?

At first people may be bothered by chronic sore throat and a low-grade fever and are likely to think they are suffering from the flu. But then comes this incredible fatigue. Only by sheer willpower do they make it through the day. As the disease progresses, cognitive impairment becomes even more of a problem than fatigue. Problems develop with memory and spatial organization. Driving becomes very hard for them. They walk into a room and wonder. "Why did I come in here?"

How is CFS diagnosed?

There is no single test for the disease, and the diagnosis is arrived at by excluding other plausible disorders. The general constellation of symptoms initially mimics mononucleosis. But what makes CFS unique is the length of time the symptoms persist. While mono generally runs its course within a period of weeks or months, CFS can drag on indefinitely.

What causes CFS?

We're not yet sure. We don't even know whether this is a new disease or an older syndrome that previously has not been adequately diagnosed. We have discovered that lots of viruses can be associated with CFS, including several strains of herpes such as Epstein-Barr, which is believed to be the most common cause of mononucleosis. But no single virus is common to all people with the disease. That leads us to suspect that possibly something goes wrong with the immune system itself.

What causes this disturbance?

One promising theory is that a retrovirus is at work. Retroviruses, so called because they reproduce themselves in a contrary manner to regular viruses, alter the genetic makeup of cells and can then thwart efforts of the immune system to combat ordinary viruses. One notorious example of a retrovirus is HIV, which causes AIDS. With AIDS, the immune system is completely destroyed. CFS is not fatal, but a similar and much less severe mechanism appears to be involved. In the presence of an ordinary virus, like herpes, the retrovirus, by disturbing immune function, increases the work the immune system has to do to rid the body of the herpes virus. It's like a car with its wheels stuck in the sand, roaring away but not moving.

Is CFS contagious?

There have been clustered outbreaks in the Lake Tahoe area, in upstate New York and elsewhere that suggest an infectious agent may be transmitted. Even so, the disease does not appear to be very contagious. Despite the fact that sufferers remain ill for years, their spouses and close contacts rarely become sick.

How are families affected by the disease?

You see relationships break up over an illness like this. Just getting out of bed in the morning can be an achievement for someone with CFS, and carrying on with normal activities at home or work becomes virtually impossible. To make matters worse, people often go for months or years without a proper diagnosis and are forced to deal with horrible uncertainty and emotional stress.

Do people ever recover from CFS?

We are hopeful that experimental drugs like Ampligen, which appears to reregulate an abnormally functioning immune system and may also have direct antiviral properties, will give people some relief from the disease, but it is still too early to judge their effectiveness. A regimen of balanced diet, adequate rest and modest physical conditioning is important for anyone who suffers from CFS. Some people do get better on their own, usually within one year of the onset of the disease. But for those with more persistent symptoms, two-thirds will substantially but not completely improve over the next two to five years. The remaining third will develop debilitating illness, which can go on indefinitely. At present there is no known cure.

Is there any good news in all this?

The growing public awareness of CFS increases the chances that people who suffer from it will get a proper diagnosis. We have noticed that when patients more fully understand the cause of their symptoms and realize that most people recover or get substantially better, they improve their chances for a return to health.