Survival characteristics of forty-three specimens of living human bone and articular cartilage from the knees of eight renal-transplant donors were studied, using a drop-tower device. Autoradiography and light and scanning electron microscopy revealed no evidence of chondrocyte death or structural damage until stress levels of twenty-five newtons per square millimeter were reached, corresponding to strains on the order of 20 to 30 per cent and involving energy absorption of one millijoule per cubic millimeter. The data for strain rates of 500 and 1000 s⁻¹ suggest that impact loads sufficient to fracture a femoral shaft of an automobile occupant are nearly sufficient to cause chondrocyte death and fissuring in the articular cartilage of either the knee or the hip if the load-bearing areas measure less than 500 square millimeters.