Seventeen months after the U.S. stimulus law authorized billions to subsidize electronic health records (EHRs), 864 pages of rules for how physicians and hospitals must show "meaningful use" of the technology are finally set. Now comes the hard part: implementing the technology in a country where, by one estimate, only 17 percent of doctors use EHRs at all.

"This is a turning point for electronic health records in America, and for improved quality and effectiveness in health care," David Blumenthal, the national coördinator for health information technology, said in a statement after the rules came out last week.

Ideally, EHRs can warn doctors against prescribing a drug that would interact badly with something a patient is already taking. Or the technology could reveal that a patient has already had a diagnostic x-ray and doesn't need another one, saving money and reducing radiation exposure. In 2006, the U.S. National Academy of Sciences' Institute of Medicine said medication errors injure 1.5 million Americans each year--and that computer systems could prevent many of these mistakes.

Such technology can also make it far easier to systematically keep track of patients with chronic conditions. For example, it could identify diabetics who have missed lab tests and appointments and may be at risk of dangerous complications that could include foot amputations.