The article discusses a new source for studying the scientific and creative biography of Evgeny Yulianovich Perfetsky – the archive of Alexey Alexandrovich Shakhmatov, which is stored in the St. Petersburg branch of the Archives of the Russian Academy of Sciences. The A.A. Shakhmatov fund contains the correspondence of scientists during the period when Perfetsky, exiled to Kholmogory for revolutionary activities among the youth, received permission to travel abroad and entered the University of Vienna, Department of Slavic Philology (the chronological framework of the correspondence covers the period from 1911–1917). The correspondence of the two Slavists has not yet received due coverage in philological or historical sciences, while it is a source for clarifying our knowledge not only about Shakhmatov’s scientific interests and his connections with fellow Slavists, but also for studying the creative legacy of Perfetsky, who made a significant contribution to the study of the Russian component in the Carpathian territories on the eve of the First World War. The article will provide an analysis of the surviving correspondence, present its main themes, and identify the progress of work on collecting materials for writing works on the history, dialectology, and ethnography of Hungarian Rus (for example, works on the religious movement in Hungarian Rus in the 16th-17th centuries, the existence of printed Old Church Slavonic books in this territory, and the problems of chronicle writing, Perfetsky’s view of which was largely influenced by Shakhmatov). © 2025 by Cherkas Global University.