Ultrasonic methods measure properties intrinsic to bone's structure that are not necessarily dependent on bone mass. Therefore, ultrasound may prove to be a useful tool for diagnosing bone fragility and osteoporosis. The goal of this study was to determine the relationship between apparent velocity of ultrasound (AVU) measured using the OsteoTechnology prototype I machine and cancellous bone yield strength (sigma y). AVU correlated well with sigma y (r = 0.753). Consistent with theory, the best predictor of cancellous bone strength was the combination of apparent density (rho a) and AVU, rho a (AVU)2, which had an r2 of 77.4%.