We have developed a photoplethysmographic technique for monitoring early signs of vascular compromise in extremities affected by direct vessel trauma, crushing trauma, or circumferential burns. The technique consists of positioning a small infrared emitter-detector array shielded from room light over a nailbed of the affected extremity and connecting the array to standard electronic monitoring equipment, thus producing a pulse tracing very similar in contour to an arterial pressure wave. In normal volunteers, simultaneous observations of the tracing and studies of muscle blood flow using Xe133 clearance showed correspondence of disappearance of the plethysmographic signal with limb-threatening levels of ischemia produced by inflation of a blood-pressure cuff. Studies comparing this technique to compartment pressures and arterial flow determined by ultrasound Doppler measurement are continuing. Clinically, we have used this monitoring technique on 29 trauma patients thus far, including 18 with circumferential full-thickness burns of at least one extremity. We believe that these preliminary studies suggest that photoplethysmography is a valuable continuous monitor of vascular status following trauma and a reliable indicator of nutritional blood flow.