In mechanical practice, a good knowledge of the mechanical properties of materials is mandatory. One of the most important properties in the actions of processing and exploitation of the material is the hardness. Due to the necessity of conducting the hardness tests on finished structures and production plants, portable devices are being developed for this purpose. The paper deals with the reliability of the results obtained using portable hardness testing devices. Tests conducted for the purpose of this thesis included hardness testing on three samples (grey cast iron SL10, austenitic steel 316L and tool steel C85W). The results obtained with a portable device for hardness testing by the rebound method (Leeb method) were compared with the results of testing by the Vickers method conducted in the Laboratory for Testing Mechanical Properties of the Faculty of Mechanical Engineering and Naval Architecture in Zagreb. The tests were performed according to the applicable standards for each method.