It is a well known fact that light emitted at a specific wavelength induces fluorescence in the human body. This kind of fluorescence is called autofluorescence. The application of autofluorescence diagnosis, on the other hand, is a more complicated system designed to detect faint autofluorescence inherent in tissues/cells. We have adopted this autofluorescence diagnosis method and developed a new autofluorescence endoscope imaging system called the SAFE-1000. Normal mucosa emitting autofluorescence appears green on the monitor, while abnormal mucosa shows a dark image caused by the lack of autofluorescence.