It is often necessary to characterize the low-frequency mechanical behavior of physiological systems. For example, the impedance describing pressure/flow characteristics is a common means of quantitating the overall mechanical behavior of the pulmonary system. The proposed work is a basic theoretical investigation into the best techniques to derive the most reliable information from the least number of experiments. A realistic mathematical "forward" model will be used to evaluate signal analysis and system identification techniques using rigorous statistical techniques. The research should lead to better technology for physiological systems identification, and it may lead to improved diagnostic procedures.