In side impacts, injury to occupants is caused by the contact of the occupant with one or more of the various interior surfaces, or structures, of the vehicle for instance, a majority of thoracic injuries are due to an impact with the interior area of the door. Likewise, a large number of head injuries result from the head striking upper interior structures.It may be possible that a change in the stiffness characteristics of these upper interior structures could reduce their injury causing potential. The first step toward improvement is the measurement of existing structural characteristics and the relation of these to head impact responses.This report reviews an approach and hardware used to measure the upper interior stiffness characteristics of a few vehicles. Alternative methods of stiffness characterization are presented. In addition, it reviews the effort made to determine the significance of the stiffness variations through an attempt to relate head injury to the measured stiffness characteristics. Injury estimates in the form of Head Injury Criteria (HIC) and Mean Strain Criteria (MSC) are presented.