Illumination of unstained 9 microns cryosections of lung tissue with 365 nm results in visible fluorescence light with a maximum intensity at about 460 nm. These fluorescence tomographical studies can be used for detecting carcinoma of the lung. The fluorescence pattern obtained can be matched nicely with histological findings. Since it takes less than 5 min for getting the fluorescence images, the fluorescence tomographical technique might be used in addition to established methods for determining the histology of a biopsy sample.