Background: The present article describes light-induced autofluorescence spectroscopy using violet-blue excitation light for endoscopic in vivo measurements in the upper GI tract. The spectra of normal mucosa, cancer, and dysplastic lesions of the esophagus and stomach are presented and compared. Methods: Over 120 spectra were obtained in 11 patients of normal mucosa and malignant lesions in the esophagus and stomach during routine endoscopy. A special light source capable of delivering either white or violet-blue light was used for the excitation of tissue auto-fluorescence via the endoscope. Endogenous fluorescence spectra emitted by the tissue were collected with a fiberoptic probe and analyzed with a spectrograph. After spectrographic measurements biopsies were taken for definitive classification of histopathologic status. Results: As compared with normal mucosa, (pre) cancerous lesions were associated with special changes in the emitted fluorescence spectra.The spectrographic records were influenced by the intensity of the illumination and on the position of the probe (distance and angle). Conclusion: Fluorescence spectroscopy with a slightly modified conventional light source might be useful for the endoscopic detection of dysplasia and early-stage carcinoma in the upper GI tract. Prospective trials need to determine the sensitivity and specificity of this new method.