In April, a startup company called Navigenics threw a swanky 10-day celebration in lower Manhattan to launch its highly publicized personal-genomics service, which offers genetic risk assessments for 21 complex health conditions--such as heart attack and diabetes--that are partly mediated by multiple genes. (I received complimentary genotyping from Navigenics; it normally costs $2,500.) Unbeknownst to attendees, the New York State Department of Health had sent a warning letter a few days earlier to the company and 22 others that offer similar products, telling them that they needed a permit before they could sell their services. New York-based party goers would be unable to partake in Navigenics' testing.

Indeed, both Navigenics and its main competitors--California's 23andMe and Iceland's deCode--have faced a stern backlash from health experts and regulators. All three companies use gene chip technology to scan an individual's genome, at a cost of $1,000 to $2,500, for variations that have been linked to diseases or to traits such as eye color and muscle strength. Understanding their risk for a disease, says Navigenics cofounder Dietrich Stephan, allows people to make plans, take preventive steps by altering their lifestyles (exercising and keeping the brain active, for example), and stay informed about new therapies. But making such tests available directly to consumers over the Internet, as these companies do, has aroused concern in both scientific and public-health circles. In their disclaimers, all three say that they are not offering medical advice or practicing medicine. But critics say that it's not just medicine, it's bad medicine.