On the basis of clinical protocols, phase II-studies have been started to evaluate photodynamic diagnosis for early visualization o cancer in bladder and lung. As tumor marker the fluorescent and photosensitizing polyporphyrin Photofrin II is used in a dose which has been proven to avoid photosensitization of the patients' skin. The drug is administered systemically in a concentration of mostly 0,4 mg/kg body weight. Fluorescence of Photofrin II in tissue is detected by an image-intensifying CCD camera coupled to endoscopes usually used in both medical disciplines. Video presentation of the marker fluorescence occurs with high contrast due to real-time image processing following two-wavelength excitation of the tissue with laser light. A keypoint of the new diagnostic method is the correlation of the fluorescence contrast and the histological examination of biopsies removed from these areas. As an examples, 87 biopsies have been taken from 17 patients suffering from bladder cancer. While all tumorous samples (n = 16) show strong fluorescence, about 30% of the biopsies are judged as false positive. A variety of premalignant diseases has been found in these sections. No false negative results have been obtained up to now.