The ability of planktonic and benthic bacteria isolated from the oligo-mesotrophic lake Jasne and the highly eutrophized, alloiotropic lake Stęgwica to utilize humic substances was studied. It was found that all the bacteria used in the experiments were able to utilize humus. The most intensive development of bacteria was observed in the presence of humic substances, which were the only source of nitrogen, it was weaker when the humic substances were the only source of carbon, and it was weakest when they were the only source of both nitrogen and carbon. The ability of planktonic and benthic bacteria isolated from lakes of different trophy to utilize humic substances is similar.