Measurement of transcutaneous oxygen perfusion through the skin is used clinically as a measure of blood flow to a region of the body, and serves as an indicative measure of wound healing potential. Topical oximetry may also be useful for tracking peripheral vascular disease (PVD). Currently, the only clinically-applied technique used for this purpose is transcutaneous oxygen monitoring (TCOM) using electrode based sensors, which require an active heating element to encourage diffusion of oxygen through the skin. Subcutaneous (2 - 3 mm below the skin surface) tissue oxygen measurements would be useful in determining blood flow in vascularized free tissue flaps used for reconstructive surgery or in tissues surrounding chronic wounds. Our group has demonstrated that biopolymer-encapsulated probes used in electron paramagnetic resonance (EPR) oximetry can be used for such applications when applied topically to the region of interest, or implanted below the skin. The use of EPR for such measurements is currently not feasible in a clinical setting due to the size, weight, and space restrictions presented by existing instrumentation. We therefore propose to design, build, and test a new, portable EPR system for clinical oximetry applications. The envisioned device will be similar to a clinical ultrasound unit, with a wand assembly that will be placed in contact with the skin to obtain oximetry measurements from the probe sensors placed on the body, or implanted just below the surface. We will use computer modeling to determine the optimum arrangement of magnets and resonator prior to construction of a working prototype device. We will then test and characterize the oxygen-sensitive probes to be used. We will then use the prototype device to quantify tissue oxygenation in a rat chronic wound model, and continue with validation measurements using the portable EPR unit on human volunteers to compare this new technology with the existing electrode-based TCOM.