In low-speed, rear-end collisions, the occupant in the target vehicle moves rearward relative to the vehicle and interacts with the seatback and seat bottom. Due to the direct interaction of the occupant with the seat, seat stiffness can affect the kinematics of the occupant. Generic seat stiffness values are often used as input parameters in computer programs, such as MADYMO, that are used to model low-speed, rear-end collisions and simulate occupant kinematics. To create an accident specific simulation, the model could take into account all aspects of the accident including the person involved, the subject vehicle, and the subject vehicle seat. Recent research has demonstrated that the seat stiffness of the compressible structure of the seat, comprised of foam and springs, can vary between vehicles, and also can vary between regions within a single vehicle seat. In order to examine the influence of seat stiffness on occupant kinematics and internal loads, MADYMO simulations were performed with a 50th percentile male Human Body Model (HBM) for a single accident sequence using seat stiffness values obtained from a variety of commercially available modern vehicles. The relevant outputs included cervical spine compressive loads and lumbar spine compressive loads. This sensitivity analysis attempts to determine the effect of vehicle seat stiffness on occupant kinematics and injury mechanics.