Photodynamic therapy (PDT) and interstitial introduction of fibers for thermotherapy are well known treatment modalities in urology. The approach of this study is to combine both techniques in an in vivo normal tissue in order to develop a selective and minimal-invasive treatment procedure for prostate carcinoma in future. Therefore, we investigated the in vivo pharmacokinetics of 5-ALA-induced PPIX in the normal dog prostate as well as its photodynamic efficacy in normal prostates in the beagle-model. Measurements of the in vivo pharmacokinetics of 5-ALA induced porphyrins by means of fiber assisted ratiofluorometry showed a maximum fluorescence intensity at time intervals of 3–4 h post administration. Fluorescence microscopy at that time showed bright specific red (or PPIX) fluorescence in epithelial cells while red fluorescence could not be observed in the stroma. Interstitial PDT using a 635-nm dye laser with an irradiation of 50 J/cm2 resulted in a non-thermic hemorrhagic lesion. The lesion size did not change significantly when an irradiation of 100 J/cm2 was used. The usefulness of PDT for treating BPH as well as prostate carcinoma has to be proven in further studies.