In this report, we discuss application of the noninvasive technology of ultraviolet fluorescence spectroscopy to the metabolic analysis of normal and compromised myocutaneous flaps. Acute changes in tissue redox states during ischemia and reperfusion were determined analysis of changes in the fluorescence spectrum of reduced nicotinomide adenine dinucleotide (NADH). Analysis of the system for NADH fluorescence showed good correlation between excitation spectra recorded at 450 nm from pure beta-NADH and those recorded from porcine rectus abdominis myocutaneous flaps. Sequential measurements of surface fluorescence were obtained from six flaps subjected to 6 hours of warm arterial ischemia and 4 hours of reperfusion. Results were compared with spectra obtained from six contralateral nonischemic control flaps. A significant mean increase in NADH fluorescence (49 percent; p < 0.05) was demonstrated within 30 minutes of vascular occlusion. Fluorescence intensity continued to increase throughout the ischemic period, reaching 320.5 percent of baseline values at 6 hours. Reperfusion resulted in the prompt return of fluorescence intensity to baseline levels. These results show that fluorescence spectroscopy of endogenous NADH is a sensitive and reliable indicator of vascular occlusion in experimental myocutaneous flaps.