A biologically safe, noninvasive method for visualizing bone and soft tissue relationships has been developed recently. Termed the ultrasonic transmission imaging system, its advantages include visualization of soft tissues in real time while motion is underway. The image can be correlated to standard x-ray films, but since no ionizing radiation is involved, repeated risk-free visualization of extremities for either diagnostic assessment or biomechanical studies is permitted. Resolution of 1 mm and a depth of field of 8 mm are adequate for visualization of neurovascular bundles, tendons, ligaments, bones, and joints. The image can be digitized and stored for later analysis on computer graphic systems. Pilot studies have correlated the ultrasonic anatomy of normal and abnormal living and cadaver hands with known anatomic structures. The benefits to biomechanical analysis include the ability to visualize and accurately measure in a noninvasive manner the in vivo changes of position of tendons and other structures during movement. These initial efforts indicate the growing diagnostic and analytic capabilities of this instrument.