AS MANAGED CARE crimps the doctor-patient relationship, it's no surprise that hordes of patients are turning to other sources of medical information -- on the Web, in self-help books, on radio call-in programs -- in the hope of doctoring themselves. It was perhaps less predictable that the side effect of this trend would be to produce big health care fortunes not for those who provide health care, nor even necessarily for those who provide health care information, but for those who help people find their way through the great slough of real and purported information that is already out there. The latest example is that prominent doctor-turned-navigator C. Everett Koop, the former surgeon general, who lent his name and imprimatur to a Web health-information site that became a stock market meteor this week after entering a partnership with America Online.

The tension between rigorous science and entrepreneurial quackery is as old as medicine. The Internet's contribution is to attract would-be entrepreneurs to both sides -- to hold out the possibility of profit from the fight against quackery as well as from the marketing of doubtful cures. Whether such profits will materialize is another matter: As anyone can see in a quick visit to the Koop site, or to other sites operated by recognized medical institutions such as the Mayo Clinic or Johns Hopkins, offering decent guidance through this thicket is a fairly labor-intensive endeavor. The Koop site, for instance, promises to rate other Internet health sites (independent estimates suggest there are at least 16,000 such sites), to lead the visitor through health news, to host question-and-answer sessions with assorted authorities and to vouch for products and services that the visitor then can buy. It also publishes editorials.

Will such sites -- odd hybrids between a publication, a doctor, a marketplace and a consumer report -- end up behaving in the marketplace more like a health care supply business (profitable), a scientific journal (unprofitable) or something new? The Web, says University of Pennsylvania medical ethicist Arthur Caplan, is "a good place to get information, not a wonderful place to get diagnosed and a terrible place to get treatment." As patients come to rely more heavily on doctor-navigators, those distinctions will take on more importance.