This project's goal is to develop a sensitive, linear, minimally invasive thermal transducer as the basis of a clinical instrument for the measurement and monitoring of tissue thermal properties, including perfusion. Tissue blood flow is one of the most important physiologic parameters and also one of the most difficult to measure. By reviewing past work on thermal probe/tissue interactions a design is proposed for an instrument whose performance is based upon optimizing the transducer response to tissue properties. It is shown that the transducer may be designed to possess a linear response to tissue thermal conductivity and perfusion, enormously simplifying the necessary analysis procedure and instrumentation. The Phase I project will address the design, fabrication and evaluation of this transducer in in vitro experiments.