Respirometric analysis of domestic sewage and textile, dairy, meat processing, tannery and confectionery wastewaters were carried out for the experimental assessment of the maximum specific growth rate of heterotrophic biomass and the correction factors for biological growth and hydrolysis under anoxic conditions. The accuracy and reliability of the experimental procedure was tested using synthetic sewage and different wastewater mixtures. The merit of adopting a lower yield coefficient associated to nitrate utilization under anoxic conditions was theoretically discussed and verified with the experimental results obtained. The kinetic basis of respirometric analysis was evaluated for interpretation of the experimental data on the basis of major mathematical methods currently defining activated sludge modelling. (C) 1998 Elsevier Science Ltd. All rights reserved.