The article examines two ancient Slavic translations of a fragment of the 3rd book of Irenaeus of Lyons On Heresies. One translation has survived as a preface to the four Gospels in a manuscript of the first third of the 15th century from the Library of the Lithuanian Academy of Sciences (fond 19, no. 6), another as part of the Izbornik 1073. Both translations were made in Eastern Bulgaria, the first contains ancient preslavisms and is very close in language to the homilies of John Chrysostom in the Codex Suprasliensis, while the second shows a tendency to replace rare preslavisms with more common equivalents. The first translation was made from the full version of the Greek text of the treatise of Irenaeus of Lyon, fully preserved to this day only in the Latin translation, and retains the author’s attribution; the second translation goes back to an abridged Greek version attributed to St. Gregory the Theologian.