The Soil microfungi in 36 northern Wisconsin conifer—hardwood forests have been surveyed by the dilution plate technique. Populations of 180 isolates from six sites in each forest examined, and frequency (sites of occurrence) was used to assess species importance. The 6,461 isolates represented 476 taxonomic entities, but only 87 (18%) of these occurred in three or more forests or had one frequency of at least 50% The principal forms in the conifer—hardwood unit were Mortierella vinacea II, Trichoderma spp., Mortierella isabellina, Penicillium nigricans, Mortierella nana, Pullularia pullulans, and Monocillium humicola var. brunneum. A few of the top—ranking conifer—hardwood microfungi are widely distributed in Wisconsin soils, others have occurred in similar types in northern and southern Wisconsin, and a third assemblage (including Mortierella vinacea II and M. nana) has been isolated only from conifer and conifer—hardwood soils in the State. An ordination, based upon compositional similarity in the microfungal communities, revealed a greatest difference between maple and hemlock soil populations. When tree importance values were superimposed on the three—dimensional microfungal ordination, spheres of occurrence were apparent for all major tree dominants. This finding confirmed the hypothesis that species composition in soil microfungal communities is correlated with vegetation, but litter calcium content, rather than the linear dry—to—mesic vegetational gradient, correlated with the first axis in the microfungal ordination. In a beech—hemlock forest soil, related densities for several dominant taxa varied with season. Both spores and hyphal fragments gave rise to colonies on the dilution plates prepared for six forest soils, and there was a direct correspondence between total colonies and numbers of germinating spores. A comparison of densities for four dominant species indicated a possible antibiotic interaction.