A loading probe for use in testing transducers includes an elongated body capable of simulating the normal acoustic impedance presented to a transducer to be tested by the medium in which the transducer is to operate. The main body of the loading probe has a tube made from a rigid material, and a rod having an elongated convergent portion extending into the interior of the tube so as to define a cavity which has a varying cross section. The cavity houses a core of material having a close match of acoustic impedance with the material of the tube and rod but a higher acoustic loss factor. The cavity is sealed. The active end of the loading probe carries a piezoelectric element having a planar form, and a protective end cap is bonded to the active end of the loading probe to enclose the piezoelectric element.