The soil microfungi associated with 26 communities of aspen (Populus tremuloides) in Saskatchewan were investigated using a dilution plate technique. Frequency values for the taxonomic entities isolated were calculated, based on occurrence at six sampling sites in each community. Most of the entities were quantitatively rare. The frequency values of the 51 commonest entities were used for quantitative analysis of microfungal community relationships by principal components analysis and by agglomerative classification. These analyses demonstrated only limited correlations of microfungal community structure and species performance with the edaphic and vegetational factors studied. The microfungal communities of aspen stands in the boreal forest region of Saskatchewan appeared to be a distinctive group characterized by the abundance ofMortierellaspp. The remaining communities, from all other parts of the province, were distinct from the boreal communities but did not form other discrete groups. Many of them contained a substantial number of species which are common grassland soil microfungi, such asFusariumspp. Almost all the common species found in aspen soils in this study have been reported previously from soil.