Wastewater generation and its subsequent treatment is a major problem for every industry and for the society as well. Prior to treatment, the wastewaters need to be monitored so as to permit their discharge into the local water resources. Amongst all the parameters for which the wastewaters are monitored, biochemical oxygen demand (BOD), is one of the most important and frequently used parameters for estimating the level of water pollution. The control of wastewater treatment plants is very difficult or even impossible using the classical determination method for BOD because of its high time consumption (3-5 days). The need for fast, portable and cost-effective methods for environmental monitoring has stimulated the production of a variety of field analytical tools such as biosensors. Biosensors are device that have several unique features such as compact size, simple to use, one step reagentless analysis, low cost and quick-real time results. The conventional BOD measurement requires 3-5 days, which a microbial BOD biosensor senses within minutes. A number of microbial BOD sensors have been developed nationally and internationally. The drawback of such developed sensors is that they cannot be used for all types of industrial and domestic wastewaters. Our developed BOD biosensor is based on a pre-tested, synergistic formulated microbial consortium. It is capable to sense the BOD load of a wide variety of synthetic as well as industrial wastewaters having low-moderate-high biodegradability within minutes. The sensor BOD values show a good linear relationship with the BOD values obtained using the conventional method upto a GGA concentration of 90 mg/l (r = 0.938). BOD values of real wastewater samples from different industries viz, distillery dairy and tannery were analysed using the developed sensor. The BOD sensor results were found to be comparable with those obtained using the conventional 3-day method. (C) 2002 Elsevier Science B.V. All rights reserved.