A method for testing the internal structure of a refractory part, has the following steps: a) by a transmission antenna, sending at least one electromagnetic wave, termed a “pulse”, into the refractory part to be tested; b) by a reception antenna, receiving the pulse after reflection thereof by a reflecting zone of the refractory part; c) analyzing the time offset between the two preceding steps in order to deduce the position, in the refractory part, of the reflecting zone, the pulse having a duration less than or equal to 0.5 nanoseconds.