The topic of this paper is diagnostics in maintenance using ultrasound. The work consists of a theoretical and a practical part. In the theoretical part, the basics of ultrasound, ultrasound diagnostics and applications of ultrasound in industry are described. The practical part of the paper was to test various bearing failures using experimental methods (Sonavu camera and bearing failure simulator). Based on the practical work, an analysis of the results was made and a conclusion was drawn on the advantages and disadvantages of this method. Ultrasonic technology is becoming increasingly important in predictive maintenance of technical systems due to condition, monitoring and reliability, thanks to the fast learning curve, simplicity due to ease of application, flexibility and rapid learning. Detecting the leakage of various reinforcing joints is one of the most common applications of ultrasound today, and it is increasingly used for the diagnosis of specific mechanical and electrical installation failures. Experimental methods help with easier navigation in practice so that the inspector knows how to recognize the type of failure on the simulator and this enables him to navigate in reality more easily. An example in this practical work was to test different bearing failures. In this way, the inspector recognizes what a bearing with a certain defect sounds like, and in this way he can recognize a broken bearing in practice.