Dr. Leroy Hood envisions the emergence of a new system of medicine he calls P4.

PREDICTIVE: Once or twice a year you'll use a handheld device that samples a drop of your blood and measures organ-specific protein levels. This will indicate whether a disease process has started ? long before symptoms appear.

You will also have your genes sequenced to identify the probability of future genetically influenced diseases.

Prognosis: A device currently under development will quantify 2,500 blood proteins. By the end of the decade, doctors will be able to sequence an individual's genes for a reasonable price.

PERSONALIZED: Massive computer systems will store detailed medical information about you and your health.

Prognosis: Far more powerful computers are needed to cost-effectively identify disease networks in humans and to store medical information on billions of individuals.

PREVENTIVE: If tests indicate that you are likely to get Parkinson's, for example, then drugs will be custom-designed to interfere with the disease networks and re-engineer them into healthy networks. If you have a 70 percent chance of getting Parkinson's, that risk might be reduced to 5 percent. Since the drugs are designed specifically for you, there will be few side effects.

Prognosis: Savings would come from attacking the disease at an early stage. But drug and insurance companies must create new business models to deal with this new approach to medicine.

PARTICIPATORY: You will decide whether to have your genes sequenced. You will be told what your probability is for acquiring different diseases, and you will choose whether to use drugs, better diet or better exercise to improve your life and health.

Prognosis: Patient education could be challenging, since patients will have to deal with complex information about their future health care.