Nitrification of ammonia in concentrated waste streams is gaining a lot of attention nowadays. Nitrosomonas europaea is the predominant ammoniaoxidizing species in these environments. Prediction of the behaviour of a pure culture of N. europaea (ATCC 19718) under conditions prevailing in concentrated waste streams was the aim of this study. The initial oxygen consumption rate of a concentrated cell suspension was used as a rapid assay to measure the effects on N. europaea under various conditions. Several relationships, based on Michaelis-Menten kinetics, were derived. They describe the behaviour of N. europaea at substrate (NH~), product (NO~-) and K +, Na ÷, SO~-, NO~-, C1-concentrations up to 500 mol/m ~ and pHs ranging from 6.5 to 8.5. High concentrations of ions inhibited N. europaea but specific substrate inhibition was not observed. Product inhibition was strongly pH-dependent and severe inhibition was found at pH 6.5.