Specimens of femoral cortical bone from normal subjects and from patients with osteoporosis were mechanically tested in tension to destruction. The osteoporotic bone showed less strength and less stiffness than the normal bone; these reductions are related to the increased cavity area in osteoporosis. Further, the osteoporotic bone is not able to absorb as much energy before fracture as the normal bone; but this difference is not related to changes in cavity area.