(FORTUNE Magazine) – Fed up with an impersonal HMO? Wondering whether your doctor really knows best? Want the full story on a disease and its treatments from people who have it? Then surf, surf, surf.

The Internet is fast emerging as the antidote to everything we hate about modern medicine. It's even saving lives--the ultimate killer app. Two years ago Clifford Sanderson, 67, asked his doctor about a pain in his right hip. Tests showed that metastasizing kidney cancer had spread to his pelvis. Sanderson, of Tyneside, England, says he was told that due to his age and advanced cancer, he could expect only "palliative care" under the British National Health Service. "I would have been lucky to last six months," he says.

With a nephew's help, he found a Website created by a patient who had beaten metastasizing kidney cancer. In a tale to make the Reaper weep, the patient, Steve Dunn of Boulder, Colo., describes on his site (www.cancerguide.org) how he cut through the medical jungle to get an experimental multidrug therapy that melted his tumors. Dunn cautions that the therapy is harsh and iffy. Undaunted, the British retiree, who has private medical coverage, found an oncologist willing to give him the same drugs. After months of self-administered injections that caused severe flulike episodes, his cancer is in remission. "It would be imprudent to anticipate more than five years without a recurrence," says Sanderson, a cheerful man who now self-administers a half-bottle of red wine each evening. But "I shall be grateful to Steve Dunn for as long as I live."

Do-it-yourself medical research got a major boost last June when the U.S. National Library of Medicine began offering free Web access to Medline (see table), its vast database of citations and abstracts from medical journals. Medline gets searched more than 250,000 times a day, says the library. Hundreds of new health-related Websites pop up each month, adds Steve Foote, an Emory University medical librarian. He maintains MedWeb, one of the largest lists of links to such sites--it recently offered some 16,000 pointers to sites on everything from strokes to "aesthetic excellence" to plastic surgery.

Caution: Quacks find the Internet ideal for linking them to credulous customers and desperate patients. Dr. John Renner of Independence, Mo., an expert on the topic, says the Web adds a tricky new twist to snake oil: Many sites that generally offer sound health information have links to ones touting bad medicine, sometimes making it hard to tell when you've crossed the border into quackery. To be sure, sites on quack cures like urine therapy seem too silly to matter. (Don't ask.) (Oh, all right--it entails drinking your own pee.) But many dubious sites make beguiling appeals to the need for hope.

Last spring Tony and Sandy Danek, residents of a Chicago suburb, turned to the Internet when their 12-year-old daughter, Elizabeth, was afflicted with bone cancer that conventional therapies couldn't stop. A Website for a group called People Against Cancer, based in the little town of Otho, Iowa, seemed to offer hope. For a $350 "donation," it submits patients' cases to a network of alternative medicine practitioners for personalized advice. The Daneks say they were "steered" by the group's network to an alternative-medicine hospital in Tijuana, Mexico, where they flew with their daughter. "They charged us $2,000 just to get in the door," says Mr. Danek. After examining Elizabeth, a doctor at the hospital "told us she had a mucous infection he knew how to treat. I thought, 'What the hell is this guy talking about?' "Hopes crushed, the family soon went home--Elizabeth died a few hours after they got back.

Says Frank Wiewel, the Iowa group's founder: "It's a tragic story. But the bottom line is that the little gal received a lot of conventional cancer therapy that didn't help." Wiewel adds that his group never recommends specific medical treatment and doesn't get paid by any practitioners. The group refunded the Daneks' $350.

Not all alternative medicine is worthless, but check Dr. Stephen Barrett's Quackwatch (www. quackwatch.com) before getting an online dose of it. Barrett offers tips for spotting "quacky" sites. Sample: Avoid ones marketing dietary supplements--although supplements are sometimes useful, Barrett says it isn't possible to run a profitable business selling them without "some form of deception."

For every cyberquack, there seem to be dozens of good medical sites. If you can't find one that fits your needs, consider Ronald Wall's strategy. Wall and his wife, of Plano, Texas, visited more than a dozen doctors as they tried to pin down a disease afflicting their daughter. After several years one finally diagnosed it as blue rubber bleb nevus syndrome, or BRBNS, which causes rubbery venous malformations. Fewer than 100 cases are known. In hope of locating enough BRBNS patients to study its cause, Wall recently co-developed a Website on the disorder with researchers at the University of Texas Southwestern Medical Center at Dallas.

Unless you're focused on a rare disease, medical surfing quickly leads to glassy-eye syndrome--the Alta Vista search engine serves up more than 95,000 Web pages mentioning "breast cancer." But there are remedies. Dunn's Cancerguide site, for instance, includes tips on how to use the Web to zero in on pertinent research. One-stop-shopping sites for specific diseases also help--a superb example can be found at rattler.cameron.edu/prostate, a prostate-cancer site spearheaded by Lawton, Okla., resident Gary Huckabay after he was diagnosed with the disease.

Disease-specific "listservs," or Internet mailing lists, can sometimes be even more helpful. They let you broadcast, via E-mail, questions to networks of patients, including ones who may know more than your doctor does about your problem. To find the mailing list you want, go to Liszt (www.liszt.com). "A lot of people deal with the anxiety about their own diseases by helping others on listservs," notes Nancy Peress, of Lewisburg, Pa., who formed a mailing list on prostate cancer after her father was diagnosed with it. Physicians often chime in too, giving some mailing lists the feel of a support group crossed with a peer-reviewed medical journal. Still, you shouldn't take online advice without consulting your doctor--he may even learn something that could help other patients.