The effect of bone-plate flexural rigidity on the strength of healing bone was explored. Plates with similar shapes and a range of flexural rigidities (from 1.4 to 16.8 Nm2) were prepared from fiber polymer composites or selected from among commercially available metal plates and applied to the anterolateral surface of osteotomized femora in dogs. At 16 wk, the plated femora and contralateral control femora were removed. Bone specimens (composed of cortex and callus) were removed from the area beneath the plate and from the opposite side of the same femur as well as from the anterolateral surface of the contralateral control femur. The strengths of these specimens were determined in bending tests. Bone strength increased with decreasing rigidity of the plate, and the effects were more marked in the specimens taken from the side of the femur opposite that of the plate. The results indicate that control of the bending loads to which bone is subjected during healing may be an important aspect of fracture treatment.