NMR spectrometer having an NMR magnet system, which comprises a permanent magnet device for generating a B 0 field in a measuring volume, and a bore through the magnet center for introducing an NMR measurement sample in a substantially cylindrical sample tube, closed at least on its underside, and having an RF coil for exciting the nuclear spins in the NMR measurement sample and having a temperature control system, the RF coil being arranged outside a cylindrical temperature control tube which extends through the measuring volume and into which the sample tube can be introduced for an NMR measurement in such a way that between the inner circumference of the cylindrical temperature control tube and the outer circumference of the sample tube there is a continuous annular air gap, through which, at least in NMR measuring operation, temperature control gas for controlling the temperature of the NMR measurement sample in the sample tube can be guided from the temperature control system through a gas inlet, characterized in that a holding device, which is movable relative to the sample tube in the measuring position thereof, is installed in the NMR spectrometer at the end of the sample tube opposite the gas inlet during NMR measuring operation, in that the holding device is designed in such a way that, in a first operating position, it does not touch the sample tube, in order to enable its introduction into its measuring position in the NMR spectrometer, in that, in a second operating position, it holds the sample tube for carrying out the NMR measurement in the measuring position thereof on its outer circumference in a force-locking and/or form-locking manner with a force or static friction F f acting axially on the sample tube, and in that, in a third operating position, it releases the sample tube again for removal from the NMR spectrometer, and in that the holding device is designed in such a way that in the second operating position, F f > F Stau − F Gewicht, where F Stau is the buoyancy force on the sample tube generated by the dynamic pressure of the temperature control gas flowing onto the sample tube during NMR measurement operation and F Gewicht is the weight of the sample tube. a holding device, which is movable relative to the sample tube in the measuring position thereof, is installed in the NMR spectrometer at the end of the sample tube opposite the gas inlet during NMR measuring operation, in that the holding device is designed in such a way that, in a first operating position, it does not touch the sample tube, in order to enable its introduction into its measuring position in the NMR spectrometer, in that, in a second operating position, it holds the sample tube for carrying out the NMR measurement in the measuring position thereof on its outer circumference in a force-locking and/or form-locking manner with a force or static friction F f acting axially on the sample tube, and in that, in a third operating position, it releases the sample tube again for removal from the NMR spectrometer, and in that the holding device is designed in such a way that in the second operating position, F f > F Stau − F Gewicht, where F Stau is the buoyancy force on the sample tube generated by the dynamic pressure of the temperature control gas flowing onto the sample tube during NMR measurement operation and F Gewicht is the weight of the sample tube.