A series of 50 amputated human lower limbs were tested to determine the injury tolerance of the ankle and foot structure to kinematic and kinetic parameters that could be used to describe the impact environment. The test apparatus consisted of a pendulum-driven plate constrained to move longitudinally while simulating the motion of the toepan structure in an automobile. The leg specimens were amputated at the midshaft of the femur and attached to a device simulating the hip joint. The legs were mounted to the plate in a position approximating the geometry typical for drivers and were constrained with a spring loaded tether and knee harness which simulated the action of the leg muscles. Pendulum speed, foot plate acceleration and loads, leg and foot angular velocities and accelerations, and tibia internal loads were measured directly for each test. The lower limb trauma included fractures of the calcaneus, talus, malleoli, and ligamentous tears identified from radiography and detailed necropsy. Logistic regression analysis was used to interpret the data. The peak plantar contad load and its rate of onset, as well as resultant heel acceleration were good predictors of injury bcO.05). The fifty percent probability of injury level using these single factor models is at 9.3 kN peak contact force, 5 kN/msec peak contact force onset rate, and 2 16 G’s peak resultant heel acceleration. Initial position of the foot was found to influence injury outcome with the dorsiflexed -foot being more resistant to injury than the neutral or plantarflexed foot. Finally, injury risk models using a linear combination of contact force or its onset rate, initial flexion angle, and resultant ankle angular velocity were found to be very good predictors of injury (p=O.OOO1).