After suffering a devastating stroke four years ago, Susan Brown was left in a wheelchair with little hope of walking again. Today, the 57-year-old Richmond, Va., woman has regained use of her legs and has begun to reclaim her life, thanks in part to encouragement she says she gets from an online “virtual world” where she can walk, run and even dance. Roberto Salvatierra, long imprisoned in his home by his terror over going outdoors, has started venturing outside more after gaining confidence by first tentatively exploring the three-dimensional, interactive world on the Internet.

John Dawley III, who has a form of autism that makes it hard to read social cues, learned how to talk with people more easily by using his computer-generated alter ego to practice with other cyber-personas.

Brown, Salvatierra and Dawley are just a few examples of an increasing number of sick, disabled and troubled people who say virtual worlds are helping them fight their diseases, live with their disabilities and sometimes even begin to recover. Researchers say they are only starting to appreciate the impact of this phenomenon.

“We’re at a major technical and social transition with this technology. It has very recently started to become a very big deal, and we haven’t by any means digested what the implications are,” said William Sims Bainbridge, a social scientist at the National Science Foundation.

In addition to helping individual patients, virtual worlds are being used for a host of other health-related purposes. Medical schools are using them to train doctors. Health departments are using them to test first responders. Researchers are using them to gain insights into how epidemics spread. Health support groups are using them to educate the public and raise money.

These increasingly sophisticated online worlds enable people to create rich virtual lives through “avatars” – identities they can tailor to their desires: Old people become young. Infirm people become vibrant. Paralyzed people become agile.

They walk, run, and even fly and “teleport” around vast realms offering shopping malls, bars, homes, parks and myriad other settings with trees swaying in the wind, fog rolling in and an occasional deer prancing past. They schmooze, flirt and comfort one another using lifelike shrugs, slouches, nods and other gestures while they type instant messages or talk directly through headsets.

Because the full-color, multifaceted nature of the experience offers so much more “emotional bandwidth” than traditional Web sites, e-mail lists and discussion groups, users say the experience can feel astonishingly real. Participants develop close relationships and share intimate details even while, paradoxically, remaining anonymous. Some say they open up in ways they never would in face-to-face encounters in real support groups, therapy sessions, or even with family and close friends in their true lives.

“You’re in this imaginary world. People don’t know much about who you really are. In that anonymity, in that almost dreamlike state, people express things about themselves they may not otherwise,” said John Suler, who studies the psychology of the Internet at Rider University in New Jersey, noting the experience can be especially useful for people with disabilities and those in remote areas where support groups or therapists are far away.

While the emergence of these worlds has generated controversy over the gender-bending, sexually outrageous, profiteering and even violent virtual behavior of some participants, their usefulness for meeting health needs has just begun to draw attention.

“There is a fundamental irony here,” said Thomas Murray of the Hastings Center, a medical ethics think tank in Garrison, N.Y. “Avatars tend to be young, beautiful, and never age or get sick. But at the same time they can serve as an important way to share information about health.”

Murray and others, however, worry that participants may neglect potentially more helpful real-life relationships, or have unrealistic expectations about what virtual worlds can do. Users and health-care providers may be rushing ahead, they say, without validating the usefulness of these worlds or identifying the dangers.

“We’ve seen the power of the Internet and what it can do,” said Albert “Skip” Rizzo, a University of Southern California psychologist who treats traumatized Iraq war veterans with virtual reality. “But as we all know there can also be negative consequences. We really need to step back and think, ‘What are the practical and ethical things we can do in the area of health, and what can’t we do?'”

The emotional punch of virtual worlds makes them fertile breeding grounds for false, misleading and possibly dangerous information. Sick, lonely and psychologically fragile people are particularly vulnerable.