There is a sharp distinction between biologic and chronologic age. One man may be sixty years old, another may be sixty years young. Chronologic age is fixed, but biologic age varies and is difficult to ascertain. Bearing in mind the fact that the various organs of the body do not age simultaneously, the difficulty of defining what is normal, and the differences between individual interpretations of tests, it becomes apparent that there is a real need for a clear-cut definition of biologic age. Dr. Benjamin has planned a health inventory for biologic age estimation in order to encourage thinking about the role biologic age plays in helping to provide an optimum life.