The aim of the study was to clarify the effect of elepidote rhododendron root fungal endophyte Calcarisporium arbuscula Preuss on the axillary shoot in vitro growth, pigment concentration and ex vitro adventitious root formation in two elepidote rhododendron cultivars, BabД«tes Lavanda and Nova Zembla. C. arbuscula mycelium fragment was added to three-month old in vitro nodal segment cultures of both cultivars. One month later leaf pigment concentration was determined spectrophotometrically, microshoot length was measured and the plants were planted for further adventitious root formation ex vitro. During the rooting, samples were collected for a further anatomical study. The length of ‘Nova Zembla’ microshoots increased significantly in the presence of C. arbuscula. The analysis showed similar tendencies of the pigment concentration in control and C. arbuscula treated microshoots of both cultivars, while in ‘Nova Zembla’ treated with the fungus the chlorophyll a concentration was significantly higher than in control. Histological study showed that C. arbuscula formed a hyphal net around the lower part of microshoots of both cultivars and hyphae were present in epidermal and cortical cells. In ‘Nova Zembla’ treated with C. arbuscula root meristemoids were formed already in vitro. In ‘BabД«tes Lavanda’ C. arbuscula treated microcuttings first meristemoids were observed on Day 5. In control microcuttings of ‘Nova Zembla’ root initial was observed on Day 9, while in ‘BabД«tes Lavanda’ processes related to adventitious root formation were not observed neither anatomically nor morphologically. At the end of the experiment fully formed roots were detected in both C. arbuscula treatment and control of ‘Nova Zembla’ and two months later all of the control and treated microcuttings of both cultivars were rooted.