||Gears perform their main task, namely load transmission, by means of very small contact areas originated by tooth interaction and thus, the analysis of phenomena occurring at the interface between mating teeth represents a critical issue in ensuring the optimal functioning of such devices. Nevertheless, while literature proposes a huge amount of numerical tooth contact analyses (TCA), a lack of experimental validation of such approaches is to be noted, since it is extremely difficult to inspect a contact interface which is, by its own nature, closed towards the outside world. One of the most promising techniques employed in investigating contact in metallic interfaces is based on the use of high frequency ultrasonic waves; their reflection from the interface (which is known to be related to contact conditions) can be graphically processed to build maps from which it is possible to assess geometrical features of the nominal contact area and, after a suitable calibration procedure, contact pressure distribution. This study proposes the application of the ultrasonic method to investigate the contact of a tooth belonging to a spur gear with a plane, thus reproducing the case of a gear-rack system. Experimental tests were carried out under different conditions, including regular contacts, misalignments and excessive waviness of the teeth; in all cases analyzed, this technique exhibited interesting capabilities in faithfully reproducing the contact features, thus allowing us to state that it may represent a useful tool in arriving at a deeper insight into contact problems in gears and, above all, in effectively validating numerical TCA and wear models.