Numerous isolates of mycorrhizal fungi from roots of the orchid Goodyera repens were identified as Rhizoctonia goodyerae-repentis and had similar characteristics in culture. All formed compatible intracellular infections in germinating seeds of G. repens but there was considerable variation in their ability to stimulate growth of seedlings. Symbiotic activity and some mycelial characteristics of isolates stored on agar and those maintained on plants changed after one year in culture. The activity of most isolates declined, but to varying extents, and the cause of this variability is not known. Two (unidentified) isolates did not establish a symbiosis with G. repens in culture.