Abstract: The invention relates to the synchronous determination of the absorption, fluorescence, dispersion and refraction of liquids, gases and solids (measurement volumes) with high sensitivity. Radiation of defined wavelength is coupled into a multiple reflection device. The transmitted coupling radiation is measured with a receiver that is located immediately behind a semireflecting mirror. The diffuse reflecting that is directed against the direction of incidence and the radiation which is specularly reflected at the boundary surface with the measurement volume are measured with a receiver that is directed at the measurement volume and located on the coupling mirror. The absorbing power is determined from the reciprocal value of the transmitted coupling radiation. The scattering power and fluorescence power are determined indirectly from the combination of diffuse reflection and transmitted radiation. The refraction is determined from the combination of specularly reflected radiation and transmitted radiation.