The detection of gastrointestinal dysplasia is an unresolved problem. Fluorescence detection of these premalignancies after exogenous application of 5-aminolevulinic acid, which is converted to protoporphyrin IX and accumulates selectively in tumors, is an interesting approach. Illumination with light of appropriate wavelength allows the discrimination and detection of gastrointestinal neoplasia either by spectroscopy or fluorescence endoscopy because of a typical red fluorescence of protoporphyrin IX. Surveillance of patients with Barrett’s esophagus and ulcerative colitis might benefit from this new technique.