The aim of this report is to introduce the scientific community to a new approach to functioning of a microbial cell-based reactor-type biosensor that could improve the selectivity of the biosensor. Summarizing the expertise in technical microbiology and in the application of microbial biosensors for basic research and taking into account the achievements in the field of miniature bioreactor development, the author offers a scheme of the formation of a microbial reactor biosensor. The author suggests to employ a miniature reactor (for continuous cultivation of a culture-receptor) in combination with the method of pulse addition (the author used this method for a 2-litre fermenter) in order to predetermine the selectivity of a biosensor (to predetermine the response of a culture-receptor).