Method for determining the contents of a fuel rod within a testing range extending in the longitudinal direction of the fuel rod, characterized by the features that(a) the position of a test coil concentrically surrounding the fuel rod is changed from the beginning to the end of the testing range, and(b) in the process, the impedance of the test coil is measured as a function of its position,(c) the test coil is fed with an a-c voltage,(d) the frequency of which is so low that the measurement value in the region of a fuel pellet of pure uranium dioxide is clearly distinguished from that which is measured in the region of a doped fuel pellet.