We are studying the use of the laser-induced fluorescence (LIF) endoscopic images of colonic mucosa for detection of pre-malignant lesions. LIF images were collected through a fiber optic colonoscope, and adenomatous polyps were used as a model of dysplasia. A total of 12 tissue samples containing 29 adenomas, obtained from colectomy specimens from 3 familial adenomatous polyposis patients, were studied. Regions of colonic mucosa were illuminated by a quartz optical fiber with near-UV light from an argon-ion laser. Autofluorescence between 400 and 700 nm was detected by means of an intensified CID camera. In the LIF images, adenomatous polyps appeared lower in intensity than normal mucosa by about a factor of 2. The LIF images were processed by dividing the raw image by a spatially averaged one to correct for differences in the distance to the tissue and in the light collection efficiency of the optics. Relative intensity thresholds were set at values varying between 55% and 90% compared to the spatial average to determine likely areas of disease. The results were compared to histology taken at 2 mm intervals along several transverse cross-sections of the specimens. At a threshold of 75%, 26 true positives, 256 true negatives, 22 false positives, and 3 false negatives were identified, resulting in a sensitivity, specificity, positive predictive value and percentage of correct determinations of 90%, 92%, 54%, and 92%, respectively. These values are comparable to results of independent diagnoses by two pathologists, demonstrating the potential of LIF to guide biopsy.