A miniscale screening system was developed to detect depolymerizing activities of fungi toward low-rank; coals, This system was suitable for the determination of changes in molecular masses as well as for the measurement of the enzymes responsible. A total of 486 fungal strains of different ecophysiological and taxonomic groups were tested for their ability to decolorize agar media containing coal-derived humic acids : 38 wood- and litter-decaying basidiomycetes caused a strong bleaching effect and 49 a weak effect, In contrast, micromycetes were proved to be unable to decolorize the coal substances. The wood-decaying fungus Nematoloma frowardii b19 most effectively bleached the medium, It could be demonstrated by; gel-permeation chromatography that the strain really depolymerizes the high molecular-mass fractions of coal humic acids by forming fulvic-acid-like compounds Extracellular enzyme activities of oxidases and peroxidases towards 2,2’-azinobis(3-ethylbenzthiazolinesulphonate) were extractable from the agar media.