The nomenclature of microscopic soil materials in soil organic horizons, as it stands, is unsuitable for modern terminology and requires revision. Soil materials are reclassified according to their mineral and organic components into five main classes_: humiskels, lithiskels, humicols, mullicols and argillicols. They are further subdivided according to the kinds of mineral grains or organic particles they contain into calcitic, feldspathic, lignic, mycetic etc., and according to structure into very coarse to extremely fine, massive, blocky, single grain, pelleted, spongy and expanded subclasses, and into fabric subclasses. Soil materials encountered in the literature are reclassified according to the revised nomenclature. © 1969.