Researchers have produced the first comprehensive genetic map of microbes that live within and upon a healthy human being, opening up new possibilities for doctors to diagnose disease and treat the sick.

The accomplishment announced Wednesday -- the result of a five-year, $173 million initiative called the Human Microbiome Project funded by the National Institutes of Health -- stems from an effort to better understand bacteria and other organisms that play a critical role in processes ranging from digestion to infection.

Scientists know the body harbors trillions of such microorganisms -- indeed, they outnumber human cells 10 to 1. But until now, they didn't know what all the bacteria were, where they were and how they might differ from person to person, or from site to site on a single body.

'This is really a new vista in biology,' said Phillip Tarr, director of pediatric gastroenterology and nutrition at Washington University School of Medicine, St. Louis, and one of the leaders of the project, which involved some 200 researchers at 80 institutions.

The new genetic map should bolster research into a number of diseases whose onset is associated with a combination of genetic predisposition and changes to the body's roster of bacteria.

'It's likely this work will lead to new treatments for [the inflammatory bowel disorder] Crohn's disease, new treatments for diabetes and metabolic diseases, new treatments for even other diseases, like eczema,' said Michael Fischbach, a biologist at the University of California, San Francisco, who wasn't involved in the project.

Dr. Fischbach cautioned that 'it's going to take a long time' before new drugs might be available, because there remains much to sort out -- not only the interplay between genetics and bacteria but also the wide variations in the bacteria on different people's bodies.

Microbes have inhabited people since the beginning of human history, researchers say. 'Most of the time we live in harmony' with them,' said Eric Green, director of the National Human Genome Research Institute. They play critical roles in digestion and other processes important for human survival.

But sometimes, the beneficialrelationship breaks down, resulting in disease.

'We need to understand better what the normal microbiome is like and what happens to it when it changes to cause or influence disease,' Dr. Green said.

The findings, reported in papers published by Nature and the Public Library of Science, were based on samples from 242 healthy volunteers in the U.S., from such sites as the mouth, nose, skin, intestine and vagina. They were analyzed with advanced versions of the DNA-sequencing machines used to map DNA in the Human Genome Project.

While that effort determined that there are about 22,000 human genes, the new project found more than eight million genes in the human microbiome -- the microorganisms living in or on the human body. It identified more than 10,000 species of microbes.

'This gives us a reference set of genes and microbes from healthy individuals,' said James Versalovic, director of the Texas Children's Microbiome Center at Baylor College of Medicine and one of the researchers on the project.

The plan is to do similar analyses of the microbiomes of children, the elderly and people from continents such as Africa and South America, as well as people with disease, to help unravel the role the microbes play in maintaining health or causing disease.