A technique for analyzing extremely small bits of genetic material shows promise for helping identify criminals from a single hair left at a crime scene, researchers reported today. The technique revealed which variant of a particular gene each of six people had, by analysis of a single hair each person had shed, the scientists wrote in the British journal Nature. John Hicks, deputy assistant director of the FBI laboratory in Washington, D.C., called the work ``very exciting.'' The technique cannot yet prove that a hair came from a particular person, but in combination with other evidence its result can be seen as ``very, very significant,'' he said. Further refinements may let it make identifications with more certainty, The work was conducted by Russell Higuchi and Henry Erlich of the Cetus Corp., of Emeryville, Calif., and George Sensabaugh and Cecilia von Beroldingen of the University of California, Berkeley. It focuses on DNA, or deoxyribonucleic acid, which forms tiny thread-like structures called chromosomes in every cell of the body. DNA consists of sequences of chemicals. Some sequences form genes, which control the activities of a cell. Details of DNA sequences vary from person to person, and researchers have exploited that fact to help solve crimes by studying such ``DNA fingerprints.'' In February, for example, a Florida jury convicted a 24-year-old man of rape after testimony that his DNA matched that found in semen left by the rapist. Hair that has been ripped from the body, as in a struggle, often contains enough living tissue in its root area for conventional DNA analysis. But more often, police recover hair that has simply fallen off a person at the crime scene, and that hair contains far less DNA, experts say. The California researchers overcame that problem by using a laboratory technique called polymerase chain reaction that created 100 billion copies of a particular portion of DNA. The ability to analyze a single hair is important, said Hicks, because that is typically all that is available at crime scenes. In addition, multiple hairs from a crime scene may have come from different people, said forensic hair expert Skip Palenik at McCrone Associates in Chicago. At present, a shed hair is examined microscopically for its physical appearance, Palenik said. But because different people can have similar-looking hairs, the new DNA technique ``represents a very important first step'' toward firm identification of people from a shed hair, he said. In the study, the researchers reported using a test to determine which of 21 versions of the ``DQ alpha'' gene is present in an individual. The gene plays a role in the disease-fighting immune system. In tests of six people, the researchers reported, a single shed hair correctly indicated which version of the gene each person had. More recent tests show success rates of 40 to 70 percent, Higuchi said in a telephone interview, adding that researchers plan to try an improved testing procedure. He said the next step is testing for more genetic characteristics, to allow greater certainty in linking a hair to a particular person. If the hair and a person share characteristics that fewer than one in 1,000 people possess, that would greatly help in making the link in court, he said. Standard DNA fingerprint techniques offer more definitive matches, with the chance of two people sharing the same DNA characteristics described as one in several billion. Hicks said that with further development, the new technique could well ``approach the fingerprint-type identifying capability. That's what we'd be looking for down the road.''