Among various mechanical faults found with an induction cage motor, the airgap eccentricity and problems affecting the bearing belong to the most frequent. Due to this fact, there has been a rapid development in methods of diagnosing the induction cage motor's condition. Non-invasive methods are generally preferred, as in most cases they do not exert any influence over the motor's work and do not ivolve making any adjustments to the motor's structure. Moreover, most of them allow the diagnostic process to be carried out when the appliance is on line. With respect to induction cage motors, the motor supply current is the main diagnostic signal which meets the above-metnioned criteria. The aim of the article is to present an innovative idea (in diagnostics), that is the possibility of using the magnetic field surrounding an induction motor as a diagnostic signal in testing rotor's eccentricity. The modelling of the magnetic field around the induction cage motor was performed by means of the ANSYS software. The simulation involved both an induction motor with eccentricity and a defect-free motor. Experimental measurements were performed in laboratory conditions.