In two of the most ancient Old Church Slavonic manuscripts, the Codex Marianus and the Codex Zographensis (10th/11th cent.), the morphologically marked vocative shows a substantial continuity with the inflectional classes by themes of Indo-European origin. From a functional or communicative point of view, the vocative case in both manuscripts is used in all contexts when required. Any evident variation in the use of the vocative as in modern Slavic languages was not detected. The few anomalies recorded concern foreign names (anthroponyms and toponyms), archaisms, such as the vocative of the adjective, or they were presumably induced by the effort to stick to the original Greek text. In general, it holds true that the morphological marking of the vocative case also depends on the philological-linguistic sensitivity of the translators themselves.