Abstract: A method for optical excitation of fluorophore-labeled DNA and fluorophore-labeled RNA, particularly of specific localizations of DNA and RNA labeled by fluorescence in situ hybridization (FISH). It is the object of the method to make possible in a simple manner a high-contrast simultaneous excitation of a plurality of FISH fluorophores which have different fluorescence characteristics and are to be detected and displayed three-dimensionally. The excitation and detection of fluorophores at a depth of the biological material greater than 100 micrometers must be ensured. The FISH fluorophores and DNA markers are excited to fluorescence by a multiphoton excitation simultaneously by pulsed and non-pulsed radiation at a single wavelength in the range between 700 nm to 1000 nm, preferably between 760 nm and 820 nm. A total of 20 commercially available FISH fluorophores and DNA markers were tested. Fluorophores which were excited simultaneously by multiphoton excitation were detected in all tested cases.