Abstract: A mixing device for the mixing of fluid measuring samples in an NMR measuring device, whereby the measuring device includes a rod (10) which is arranged coaxially to the main field magnet coil of the NMR measuring device to be movable in the axial direction and, on one end, exhibits a piston projecting into the measuring sample and, with the assistance of a drive coil (8) arranged at the end facing away from the measuring sample, is moved in the axial direction when current flows through the drive coil (8), wherein a spring element (7) is provided to move the rod (10) into a rest position when no current flows through the drive coil (8), is characterized by the drive coil (8) being arranged, in an axially movable fashion, in the inhomogeneous region of the magnetic field produced by the main field magnet coil coaxial to the main field magnet coil, the drive coil (8), on one axial end, being rigidly connected to the rod (10) and, on the end facing away from the rod (10), being connected, via the spring element