A new method is developed for the respirometric assessment of the soluble and particulate COD components in wastewater. The method relies on evaluating the area under the oxygen uptake rate (OUR) curve, excluding the fraction associated with endogenous respiration, generated for a wastewater sample as the equivalent of its biodegradable COD content. The method compares well with a previously recommended procedure for the calculation of the soluble inert COD. It also enables the computation of the soluble residual microbial products likely to be generated during the course of biological processes. (C) 2003 Elsevier Science Inc. All rights reserved.