Fluorescence spectra of dermal lesions on 48 rats were investigated using excitation wavelengths of 275, 300, and 340 nm. Emissions at 340 and 460 nm were measured in both the forequarter and hindquarter lesions as function of time after incision. Unlike the 460-nm emission, intensity at 340 nm increased with time and then saturated. Control studies on intact skin and lesions in dead rats failed to demonstrate any time-dependent changes at these wavelengths. It appears that the increase in the 340-nm intensity is due to changes in the tryptophan level, and may reflect accumulation of fibrinogen in the early wound healing process.