The nitrogen utilization requirement (NUR) test is a useful respirometric procedure for the assessment of major kinetic constants in activated sludge systems designed for nitrogen removal. The electron transfer mechanism of nitrogenous compounds often involves significant nitrite accumulation which impairs the accuracy of the NUR test. Experimental results revealed no meaningful correlation between nitrite accumulation and the initial nitrate concentration or the food/microorganism (F/M) ratio. Significant impact of nitrite accumulation was observed both on the assessment of the readily biodegradable COD component, the correction factor for anoxic growth and the denitrification rates applicable to domestic sewage and a number of industrial wastewaters.