Visual detection of tumors, especially during the early stages, is expected to be improved considerably by examining the fluorescence either of tumor-selective exogenous dyes such as protoporphyrin IX, induced by 5-aminolevulinic acid, or by analyzing the autofluorescent properties of healthy and neoplastic tissue. The present paper describes technical devices using light sources for fluorescence excitation, and sensitive detection systems such as intensified cameras and optical multichannel analyzers used for fiber-assisted point measurements. In the discussion of these systems, special consideration is given to their commercial availability and potential for endoscopic applications in the gastrointestinal tract. In this clinical discipline, the major interest lies in the ability to locate malignancies in the esophagus and colon. In recent years, there has been increasing clinical experience in this area, particularly in detecting adenocarcinoma in Barrett's esophagus and malignant alterations in the colon, such as in ulcerative colitis and polyps. Although several research groups have reported sensitivities and specificities for fluorescence gastroscopy of more than 80%, the potential benefits of the technique to patients need to be evaluated in further clinical studies.