The fluorescence monitoring represents an innovative approach to detect tumor tissue by photosensitizer-mediated fluorescence. Therefore, information on cellular uptake, tumor selectivity and accumulation properties of photosensitizers are of essential interest. In this study we compared the accumulation properties of two photosensitizer precursors, the 5-aminolaevulinic acid (ALA) and a hexylester of ALA (h-ALA), in vivo using the hen's egg model and the human larynx carcinoma cell line HEp-2. The formation of the actual photosensitizer, protoporphyrin IX (PpIX), was determined both qualitatively and quantitatively. The intensity of the excited PpIX-fluorescence was observed as an indicator for the presence of PpIX after topical ALA- and h-ALA-applications. PpIX-fluorescence was measured using spatially resolved fluorescence spectroscopy.