The system for measuring a magnetic resonance signal within a sample (4) placed in a static external magnetic field (H) includes an excitation device (1 to 3, 6 to 10) for applying high-intensity radio-frequency pulses at a predetermined emission frequency f.sub.e in a measurement zone containing the sample (4). The excitation device includes an excitation coil (3) tuned to the predetermined emission frequency f.sub.e and disposed in the vicinity of the sample (4) in such a way as to produce an electromagnetic field essentially perpendicular to the static external magnetic field (H). The system further includes at least a superconductive-magnetoresistive hybrid sensor (5) including a superconductive loop having a constriction adapted to increase significantly the current density and at least a magnetoresistive sensor placed in the immediate vicinity of said constriction (72) and being separated therefrom by an insulative deposit.