Prerequisite for the enhanced biological phosphorus removal in activated sludge plants are temporary anaerobic (nitrate and oxygen-free) conditions. The carbon substrates absorbed during this period are, under anoxic or aerobic conditions, utilised by the corresponding organisms for growing. Parallel to this, under anaerobic conditions, a large increase in the phosphorus concentration can be observed which decreases again during growth. The phosphorus-netto elimination obtained depends on the substrate available in the anaerobic phase. A pilot plant in Zurich operated with communal sewage showed an average phosphorus elimination capacity of 5.6 gP/m3influence. Detailed investigations with artificially increased phosphorus pattern resulted in characteristic weekly pattern, with distinct phosphorus discharge peaks after weekends or rainy periods. Combined with the enhanced biological phosphorus removal was a good denitrification performance. A prerequisite for the integration of an enhanced biological phosphorus removal in a sewage treatment plant is due to the biologic character of the process, a good understanding of the processes and their interactions. Economic advantages will result, above all, through the reduced amount of sludge produced (30-60% compared with the chemical precipitation) but also through the distinctly reduced chemicals requirement.