A miniature bioreactor was fabricated as a contactor between biosensing cells and toxic materials. This miniature bioreactor (58 mt working volume) showed performance similar to that of a conventional bioreactor, as well as the advantages of easy installation, facile operation, and small medium requirements during long-term continuous operation. A performance evaluation measured the response to ethanol in continuous operation by using a recombinant bioluminescent Escherichia coli strain. Continuous cultures were repeatedly induced by the ethanol challenge. Steady-state cell concentrations (OD) were found to be decreased, the induced specific bioluminescence (SBL) peak value was found to be increased, and the peak response time, which is the time constant of this continuous monitoring system, was found to be decreased with increasing dilution rate. Finally, on- and off-line bioluminescence monitoring was shown to be reliable, suggesting that this system is suitable for applications such as monitoring the influent and effluent streams of waste water biotreatment plants.