Ultrasonic velocity measurement in bone can be used as a clinical tool that will accurately and objectively monitor the progress of fracture healing. This technique may provide a rational basis for evaluating the effectiveness of various modalities in clinical treatment. The eventual goal of this technique is to determine the status of healing fractures, prescribe appropriate treatment, give the rationale for the timing and form of a rehabilitative program that would accelerate the patient's return to productivity. An instrument has been developed to measure ultrasonic velocity in the long bones of the extremities. Serial measurements of tibial fractures and the measurement of a large group of normals shows no statistically significant differences in ultrasonic measurements have been found on the basis of race, sex, or pregnancy among normals. But a numerically small but statistically significant variation with age was found. While the number of fracture cases observed was small, the evidence is clear that ultrasonic measurement in fractured tibia may give a more reliable indication of the general pattern of healing response than the clinical and roentgenographic examination.