In addition to biodiversity research, studies of endemism and analyses of the organisms associated with endemic taxa are also of great importance (Horchakovskyi, 1963). "Medobory Nature Reserve" (Ukraine, Ternopil Oblast) has a rich endemic and relict flora. Betula klokovii has a very restricted range, being known only from the Strahova and Maslyatin hills in the western part of Krementsy range (the "Kremenitsky Hory" section of the reserve). It is found in specific steppe and meadow-steppe plant communities, on warm calcareous rocks, growing on calcareous soils, and "sarmatsky" sandy soils which are naturally enriched with calcium (Zaveryukha, 1985). There appears to have been no previous research on wood-inhabiting fungi on this species, and during our research we have generated 15 records of 8 ascomycete species. Six were conidial. Along with the common birch-inhabiting fungi Libertella betulina Desm. and Prosthemium betulinum Kunze (Girzhits'ka, 1927; Girzhits'ka, 1929), we found Dothiorella betulae (Preus.) Sacc., previously known in Ukraine only from western Polissya (Solomakina, 1959). Our record of the hyphomycete Sporidesmium elegans appears to be the first from western Ukraine. We also recorded the coelomycetes Phoma corticola Preuss which has previously been collected only in Prykarpatia (Merezhko, 1991), and Haplosporella conglobata (Sacc.) Allesch. known hitherto only from Crimea (Merezhko, 1987). The most abundant teleomorphic ascomycete on Betula klokovii was Diatrypella favacea (Fr.) Ces. & De Not. Diatrypella melaena Nits. was also found. Both are quite widespread in Ukraine.