The determination of the nature of diffuse liver diseases is critical to patient management. At present, only invasive and limited non-invasive methods are available for reliable diagnosis. The objective of this research is to demonstrate the feasibility of identification and differentiation of normal and diffusely diseased livers in vivo using noninvasive ultrasonic pulse-echo methods. Specifically, this is achieved by accurately measuring the speed of sound propagation in these tissues. The literature suggests that certain diffuse liver diseases can be differentiated from normals in vitro and in vivo, based on the speed of sound propagation. Since the speed of sound in pathological tissues varies by up to a few percent only, accurate methods for its measurement must be found. We have recently developed a pulse echo Beam Tracking technique which is capable of such accurate measurements. Our preliminary computer simulations and in vitro studies show that the speed of sound estimates so obtained in relatively small regions is essentially unbiased and highly precise. The first phase of the research will involve the establishment of the optimal experimental conditions under which the beam tracking technique should be used. This will be done via computer simulations. The second phase will involve design and construction of a dual purpose Beam Tracking System which is suitable for rapid in vitro and in vivo speed of sound estimations. The third phase will include measurements of the speed of sound parameter in known normal and diffusely diseased liver specimens in vitro using both classical methods and the Beam Tracking System. Extent of disease will be pathologically and biochemically confirmed. Finally, in the fourth phase the Beam Tracking apparatus will be used to make speed of sound estimations in normal and biopsy proved diseased livers in vivo. The in vivo speed of sound values will be compared to the previously archived values obtained from the in vitro studies.