The study tests the hypothesis according to which the Slavic anthroponyms in -e and -o underwent evolution from vocative endings to hypocoristic derivative suffixes and then to anthroponymic formants. According to the Author, such a hypothesis can be considered entirely plausible, albeit only as a mechanism of formation parallel to and intertwined with other processes of morphemic function change. As a phenomenon observable in both diachrony and synchrony, categorial lability between vocative and word formation can thus be considered inherent in the system of Slavic languages. However the anthroponyms in -e and -o have had different diffusion and distribution in the various Slavic languages and today occupy dissimilar places within the system and varieties of each language.