Having tackled some of the classic single-gene diseases like Tay-Sachs, sickle cell, or Huntington's disease in a previous volume (Heredity and You, 1974) the authors (she, a science writer; he, the former Director of Clinical Laboratories at Brookdale Hospital in Brooklyn) felt impelled to discuss conditions where heredity is important, but not decisive. In short, where genes need not rule destiny. Such conditions include coronary heart disease, high blood pressure, diabetes, obesity, and aging. Their contention is that if tests show familial hyperlipidemia or hypercholesterolemia (which predisposes to arteriosclerosis), you can do something about it, especially if you start early in life. Judicious diet, exercise, relaxation, or, if necessary, cholesterol-lowering drugs may be completely preventative. So, too, adjustments in lifestyle and appropriate medication may eliminate hypertension, diabetes, or obesity. Knowledge of the exact genetic or environmental components in any disease is far from complete of course; and the authors round out their discussion with a survey of current theories and therapeutic approaches. (For example, soft water, salt, and a variety of other substances probably contribute to high blood pressure; a ""slow"" virus may be implicated in diabetes.) The long chapters might better have been subdivided and summarized; the authors have a habit of changing topics in midstream and the documentation intrudes on the narrative. The overall approach is fine, however. Soon, we're advised, most conditions of health or disease will be regarded as ""genvironmental""--a view which should encourage individuals to more active participation in caring for themselves and their surrounds.