Fifty-five soil samples, from 21 geographic locations in seven countries, from whichHistoplasma capsulatumwas isolated were analyzed mineralogically by X-ray diffraction techniques. None of the soils, excepting two from a site from Italy, contained swelling, three-layer clay minerals that expanded beyond 14 Å when homoionic to K, air-dried, and saturated with glycerol. Presence of the fungus was not related to the presence or absence of other clay mineral species or to soil pH. These results were similar to those obtained withFusariumwilt of banana, in that rate of spread of the wilt was rapid in soils not containing such swelling three-layer silicates but was slow in soils that contained them. These observations, together with those demonstrating that various clay minerals differentially influence growth and activity of bacteria and fungi, suggest that the distribution in soil of this human pathogen is influenced by the type of clay minerals present.