Photodynamic therapy is a promising method for diagnostics and treatment of cancers of varying localization. Photodynamic diagnostic systems are based on fluorescence detection of photosensitizers. One of the much used photosensitizers is photoditazin, but it is characterized by too small fluorescence-absorption spectral separation. This property involves considerable difficulties in spectral selection of fluorescent emission and exciting laser radiation when working out diagnostic systems. Optical properties of photoditazin have been studied in this work. The absorption spectra were recorded to refine the spectral positions of line maxima. The efficient fluorescence in the spectral range between 670 and 800 nm was found to be obtainable under radiant excitation with not only conventional wavelength (660 nm) but with 405 nm wavelength as well. If the latter is the case the spectral selection of exciting radiation and fluorescent emission becomes much simpler. The studies conducted allowed us to determine requirements for spectral optical elements of photodynamic diagnostic systems. The fluorescence excitation with laser radiation at 405 nm wavelength was shown to be available for diagnostic systems with limited depth of light penetration into tissue.