Alcohol has long been known to play a role in suicides, but there have been little data regarding which victims use it and how often. Now the federal Centers for Disease Control and Prevention reports that in a large sample of suicide victims whose blood alcohol levels were measured post mortem, one in four had been legally drunk, with a blood alcohol content at or above the federal standard of 0.08, or 8 milligrams of alcohol per 100 milliliters of blood.

The study's findings were limited because it examined data from only 17 states and because blood alcohol measurements were available for only 70 percent of those who committed suicide in those states. Still, about one-third of those tested had some level of alcohol in their bloodstream at death, the researchers found.

"Alcohol is a component of suicidal behavior," said Dr. Alex Crosby, author of the report published on Thursday in the C.D.C.'s Morbidity and Mortality Weekly Report. "It leads to disinhibition, and it can enhance feelings of hopelessness and depression. Alcohol impairs judgment and can lead to much more impulsive behavior."

"Any suicide prevention efforts must take that into account and address alcohol and substance abuse as well," he added.

The study was among the first to analyze the role alcohol plays in suicide among different racial and ethnic groups. It found that American Indians and Alaska Natives were most likely to have been drunk when they committed suicide, with 37 percent legally intoxicated at the time of death. Among Hispanics, 29 percent were legally intoxicated when they took their lives.

But, Dr. Crosby emphasized, "The most important finding is that alcohol was linked to suicide across all the groups."

Younger adults and men were more likely than women or older people to have been drunk, the study found. Some 28 percent of adults ages 20 to 49 were intoxicated when they committed suicide, and 25 percent of men were intoxicated, compared to 18 percent of women.

The analysis was done by the agency's division of violence prevention. Researchers examined data on 19,255 suicides from 17 states that contributed data to the National Violent Death Reporting System during 2005 and 2006.

Other experts suggested alcohol may play an even more prominent role in suicide in some regions than the study suggests. Dr. Philip A. May, professor of sociology at the University of New Mexico in Albuquerque, said alcohol plays a role in about 40 percent of suicides in New Mexico.

"The younger the individual, no matter what ethnic group, the more impulsive the suicide is, and the more impulsive the suicide is, the more likely alcohol is a major factor or trigger," Dr. May said.

The typical scenario is that a young adult who is already troubled suffers a setback, such as a job loss or the breakup of a relationship, and starts binge drinking. "It's unclear if they get drunk in order to commit suicide, or that when they're drunk they are more likely to do it," Dr. May said. "Intoxication may be turned to as a solution but might ultimately trigger the ultimate solution for them - that is, killing themselves."