Fluorescence spectroscopy and microscopy are important techniques in molecular biology. However, for their application highly fluorescent dyes have to be introduced into a sample. On the one hand, this changes the sample properties, while on the other hand one has to face the problem of dye photobleaching. We therefore developed Coherent Anti-Stokes Raman Scattering (CARS) microscopy as a sensitive detection method which uses molecular vibration spectra for selective contrast generation. For this reason it works without the external labelling. While standard vibrational spectroscopic methods either do not offer high sensitivity (IR microscopy) or afford high excitation intensities (Raman microscopy), CARS-microscopy offers high sensitivity and three dimensional resolution comparable to two-photon microscopy. It is therefore ideally suited for the spatially resolved imaging of small, physiologically important molecules in live cells.