Abstract: A probe head for nuclear magnetic resonance measurements is disclosed in which at least a first kind of nuclei with a first, higher resonance frequency and a second kind of nuclei with a second, lower resonance frequency are excited within a magnetic field. The probe head comprises a first input/output terminal for the higher resonance frequency and a second input/output terminal for the lower resonance frequency. A measuring coil cooperates with a sample. The measuring coil has a first terminal end and a second terminal end. The first terminal end is coupled to the first input/output terminal and the second terminal end is coupled to the second input/output terminal. A stop circuit tuned to signals of the higher resonance frequency is arranged between the second terminal end and the second input/output terminal. The stop circuit, further, comprises a line having a length equalling a quarter wave length of the higher resonance frequency. The first line is arranged in series with the measuring coil.