Still, the conclusion was a blow to veterans who for years have maintained that exposures to pesticides, weapons residues or other chemicals caused a set of symptoms unique to their service in Operation Desert Storm.

A range of symptoms including fatigue, joint and muscle pain, and gastrointestinal, respiratory, cognitive and skin problems have become collectively known to many Americans as "Gulf War Syndrome." But experts convened by the IOM said their review of 850 studies shows such a syndrome does not, in fact, exist.

While studies put Gulf War veterans at higher risk than non-deployed soldiers for a variety of illnesses, "the results of that research indicate that ... there is not a unique symptom complex (or syndrome) in deployed Gulf War veterans," the report stated.

Congress and the Veterans Administration rely in part on IOM to determine compensation levels for various illnesses. The VA has resisted calls to classify Gulf War symptoms as a service-connected syndrome. Tuesday's conclusions appear to make it more unlikely that soldiers will be able to prove to the government's satisfaction that their symptoms are a result of service in Iraq and therefore deserving of full compensation.

"It makes it much harder to make that case," Shannon Middleton, assistant director of health policy at the American Legion, said in an interview.

Thirty percent of Gulf War veterans complain of some form of "multi-symptom" illness, often including fatigue, depression, anxiety, pain or gastrointestinal problems. About half as many non-deployed veterans complain of those symptoms, according to the report.

The Pentagon began ordering soldiers to undergo health evaluations before deployment in the 1990s after complaints about Gulf War Illness first surfaced. But earlier studies usually lacked control groups or measures of soldiers' health before the war, factors researchers consider vital to understanding the cause of disease.

Complaints of respiratory and cardiovascular symptoms, while more frequent in combat veterans, were not generally borne out by physiological tests of heart and lung function.

"They're not different from the symptoms deployed people have. They just report them at a higher rate," Dr. Lynn R. Goldman, a professor at the Bloomberg School of Public Health at Johns Hopkins University and chair of the IOM panel, said in an interview.

The report did validate the higher rates of depression, anxiety, post-traumatic stress and substance abuse often seen in combat veterans and those with prolonged service in battle theaters.

The results angered some Gulf War activists. Joyce Riley, spokeswoman for the American Gulf War Veterans Association, called the report "one more blow" for soldiers returned from the war.

That group and others maintain that as many as 150,000 Gulf War veterans suffer from disabling symptoms unique to their service in Iraq and Kuwait but that full compensation remains out of reach.

Riley called the debate over a definition of Gulf War Syndrome "meaningless."

"Are they sick, or are they not sick?" she asked.

Riley, a former Air Force captain who served in the Gulf War as a nurse, accused the IOM panel of reaching a conclusion designed to prevent expense and embarrassment for the U.S. government.

"They don't want to have a diagnosis that the VA would have to cover," she said.

In response, Goldman praised the panel of medical and statistical experts for their "intellectual integrity, scientific integrity."

Some studies found increased rates of birth defects in children of soldiers, though results are inconsistent. Of those that have been observed, urinary-tract abnormalities are the most consistent, the report said.

The report also cited studies linking Gulf War service to a few diseases, including the rare but fatal nerve disorder ALS, also known as Lou Gehrig's disease. Experts urged the department to perform follow-up studies on possible ALS, birth defects, some cancers and a suspected higher rate of motor-vehicle deaths in Gulf veterans.

Some troops also showed evidence of cognitive symptoms consistent with exposure to sarin, a nerve agent used in chemical weapons that were destroyed by U.S. forces at Khamisiyah, Iraq, during the war.

"We don't really clearly know who was exposed to sarin gas and who wasn't. We don't know for sure that anyone was. A few measurements on the ground would have helped tremendously. That is what we are recommending for the future," Goldman said.

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