The master’s thesis points out that the care for Slovene language is legally protected as the key element of Slovenian national and cultural identity. By law, the state has to attend to Slovene language, therefore the opera, as a state cultural institution, employs theatre proofreaders. The master’s thesis presents their assignments with an emphasis on the role of speech consultant, and suggests their new naming - opera proofreader. Sung opera text needs to be intelligible, a justified cause for an exception being only a great tonal height and ensemble opera movements. The opera proofreader has to be professionally educated in linguistic and musical fields: the articulation of Slovene literary language sounds in opera singing depends on the linguistic norm and musical laws. The musical elements influence the suprasegmental properties of the vowels, while the acoustic laws affect the incomprehensiveness of the vowels in a high tonal position. The vowels are the carriers of the musical phrase. The sonorants must be enhanced, and different pronunciation rules apply for the obstruents in regard to individual category of their division: plosives are pronounced softly, alveolar and postalveolar affricates and fricatives are emphasised according to sonority, permanent sounds are not stretched, but an as frontal pronunciation spot as possible applies to all. Practical examples from the opera The Bartered Bride by Bedřich Smetana illustrate theoretical assertions.