On the TV show House, Dr. Gregory House spends most of each hourlong episode wrestling with how to diagnose a patient who presents a bewildering set of symptoms.

IBM research engineer Steve Daniels jokes that he and his colleagues could turn House into a "five-second show." The doctors would simply ask, "Hey, Watson, what does this guy have?"

Watson is the supercomputing engine that beat the top two human competitors on the quiz show Jeopardy! this year, and Daniels is on the IBM team developing the software's first commercial application as what could be a stunningly useful diagnostic assistant for doctors. If it works as envisioned, Watson could help doctors identify what is afflicting any patient and suggest a course of treatment.

With Watson, the company is also experimenting with a new business model: knowledge-as-a-service. Within two years, IBM says, it will begin charging health-care practitioners to log in to computers running the Watson software so they can get help cracking tough medical questions or finding the most cost-effective treatment.

A "Dr. Watson" would not be the first automated diagnostic tool; other online systems are already available to walk physicians through lists of suggestions for what might be ailing a patient. However, IBM researchers believe Watson will outshine the others because it can automatically digest not only textbook medical knowledge (the software can read one million books in three seconds) but also patient blogs, insurance claims, and millions of observations that doctors are increasingly being asked to encode into electronic patient records.

IBM says Watson can't replace doctors, yet behind Watson and other automated diagnostic tools is a recognition that no human can keep up with expanding medical knowledge. New treatments and new subcategories of disease are constantly being discovered, and even long-documented illnesses might be so rare that most doctors would never have encountered a case before.