An ATR-probe including: a housing having a media opening; a radiation guiding body closing the media opening and having two planparallel surfaces, between which light can be guided by means of total reflection. A section of a first planparallel surface bordered by a sealing ring can be contacted through the media opening with a medium to be measured. Transmission light conductors and receiving light conductors in the housing, wherein light is guided from the transmission light conductors, through the radiation guiding body, into the receiving light conductors; and wherein adjoining the first planparallel surface are first and second deflection surfaces, on which, respectively, light coupled into the radiation guiding body and light to be coupled out are deflected by total reflection, so that the light can be guided between the planparallel surfaces by means of total reflection. The light is not collimated, and the effective area of the transmission light conductors is smaller than the effective area of the receiving light conductors.