Two strains of bacteria isolated from activated sludge were tested for their ability to grow under aerobic, anaerobic and denitrifying condition.The microorganisms stored phosphorus intracellulary as polyphosphates in aerobic and anoxic mileu.Both strains appared to be able to release phosphates anaerobicaly, which was stimulated by acetate.Particularly high P-relaese effect was observed in the case of bacteria which grew under anoxic conditions.