A pediatrician's personal influence by brief and casual discussion during a routine office visit has been demonstrated by this controlled study to be effective. Installation of seat belts was used to demonstrate this effectiveness. In 1964 all new cars will be equipped with seat belts so this problem may no longer need attention. Nevertheless, personal influence is an effective and powerful tool. When properly applied it can result in rich benefits for the patient and equally rich satisfaction for the pediatrician. It is the duty of all physicians to use this effective tool in the many areas of his practice.