The aim of a functional prosthesis - a hearing aid - is to improve the comprehensibility of speech. The hearing aid is individually adjusted for the patient. Every deaf patient is subjected first to an extensive otolaryngological and audiological examination programme which comprises the recording of the case-history, assessment of the ENT diagnosis, examinations of threshold and suprathreshold sound audiometry, verbal and sentence audiometry in a sound-proof chamber and in space. To set the most important parameters of hearing aids (frequency characteristics, intensification and dynamic range) directly on the patient's ear, in the ENT department of the health centre of the Uranium Industry in Príbram Rastronics equipment from Denmark is used which makes it possible to achieve optimal adjustment of hearing aids, using several calculations applied on an international scale.