Respirometric analysis of domestic sewage together with textile, dairy, meat processing, tannery and confectionery wastewaters were carried out for the experimental assessment of the readily biodegradable GOD. The accuracy and the reliability of the experimental procedure was tested using synthetic sewage and different wastewater mixtures. The merit of OUR and NUR measurements was investigated in parallel aerobic and anoxic batch reactors. The OUR data was analysed with specific emphasis to identify the lower plateau associated with the hydrolysis of slowly biodegradable substrate. The NUR data was corrected for nitrite formation to provide an accurate account of electron acceptor consumption. The respirometric procedure and especially the effect of the initial substrate to biomass F/M (C-T1/X-T1) ratio was investigated using model simulation of the respirometry curve together with the collected experimental data. (C) 1998 Elsevier Science Ltd. All rights reserved.