Abstract: A noninvasive method of testing the integrity of an in vivo bone, to determine either the possible existence of a fracture or the progress of healing of a fracture, comprises placing an electrical vibration transducer against the exterior of the soft tissue surrounding the bone, including a mechanical vibration in the bone by striking it with a reflex hammer, and producing an electrical signal from the transducer representative of the mechanical vibration thus induced in the bone. The resonant frequency and the energy concentration at the resonant frequency exhibited by the mechanical vibration are both determined from the electrical signal, and first visual indicia variably responsive to the resonant frequency and second visual indicia variably responsive to the energy concentration are displayed.