The microbiological analysis of soils from Ontario, Yukon, and Northwest Territories showed the presence of manganese-oxidizing bacteria, Actinomycetes, and fungi. Bacteria and Actinomycetes were predominant in boreal and tundra soils whereas fungi were predominant in the Ontario samples. The 18 species of fungi studied were able to oxidize 10 different compounds of manganese including a chelated form as well as an organic Mn2+ complex. Coniothyrium fuckelii, Periconia sp., P. circinata, P. macrospinosa, Phoma sp., and Sporothrix sp. oxidized all 10 Mn2+ compounds tested. One bacterial culture isolated from Arctic soil was able to oxidize only Mn2+ acetate and tartrate salts.The addition to Mn2+ sulfate medium of either calcium salts of several organic acids or various carbohydrates affected the growth of fungi as well as the nature of the end product of Mn2+ oxidation. Thus, the manganic granules produced by Cephalosporium sp. in the medium in the presence of glucose or starch were resistant to solubilization, dissolving only after 6 h in 1 N ammonium acetate (pH 7.0) containing 0.2% of hydroquinone. Granules produced by P. circinata in the presence of cellulose were insoluble in this solvent. On dissolution of the granules with 30% hydrochloric acid, the residue did not show the presence of bacteria under microscopic examination.