The message is prevention, the medium is profiling, and it just may be the wave of the future. The procedure, moreover, is simple. First, you fill out a detailed health questionnaire (sample supplied), which solicits data on blood, family history, life style, etc.; and on this basis, you can compute your ""medical age,"" along with your chances of dying from various causes over the coming decade. As a bonus, there are also estimates of how many years you can add (or to what degree risk can be reduced) by changing the changeable--your weight, smoking habits, and so on. The technique is grounded in the efforts of public health personnel, statisticians, and preventive-medicine physicians who, in chronicling the epidemiological figures, have noted to how great an extent disease is postponable if not preventable. (The authors cite Dr. Lewis Robbins, in particular, as the developer of the first profiling method, in the 1950s, and as a pioneer in the Framingham, Mass., heart study.) There are now a number of computer centers in the country, too, prepared to analyze questionnaires submitted by individuals or groups, and to supply computer printouts under strict confidentiality rules. For the motivated, the profile can, it appears, be a strong incentive to change. The authors have included a savvy chapter on the general problem of habit change and some fine three-dimensional case histories. Among our favorites: the nurse who overcame a truly astonishing alcohol habit, the doctor who quit smoking just before his lung-cancer surgery, and the 86-year-old toughie with two mastectomies behind her who said, ""I'm so well, I'm dull."" A sophisticated approach that's also common sense.