Biosensors are analytical devices for selective detection of an analyte or a group of analytes that combine biological material with a physicochemical detector, yielding a measurable signal. Biosensors are used in various fields of human activity, including environmental and clinical analyses, food analyses and control of industrial processes. Most efforts in biosensor studies have been focused on the fabrication of various combinations of biological components and measuring systems; less attention has been paid to the interpretation of factors, affecting the formation of biosensor output signal and the problems of biosensor calibration. So in many cases only a fraction of potentially available information is taken into consideration, making the biosensor analyses less reliable than they actually could be. The present work is an effort to solve some of the problems in biosensor signal analysis, proposing a new approach to signal modelling and calibration of biosensors, based on oxidoreductases; just to promote the application of these biosensors for on-line analyses.