The activated sludge respiration measurement is proposed for assessing the activated sludge processes and biological treatability of wastewaters. Different municipal and industrial wastewaters influents to the Kohtla-Jarve wastewater treatment plant were analysed and compared on the basis of exogenous oxygen uptake rates of activated sludge. The kinetic parameters of biodegradation processes were determined by monitoring the degradation-associated oxygen consumption in tests with different amounts of wastewaters and simple biokinetic model of activated sludge respiration.