In the indirect impedancemetry technique, the CO2 produced during biological activity reacts with potassium hydroxide (KOH) solution, providing negative conductance variation. In this work, this technique was optimized, on a rapid automated bacterial impedance technique (RABIT) apparatus, developed by Don Whitley Sc. Ltd (UK). The KOH concentration and volume, as well as the temperature were tested. The dynamics of CO2 absorption and the ratio between the conductance variation and the amount of CO2 produced were examined. After injection of CO2 either directly in the KOH solution, or above the KOH solution, the best results were obtained with a KOH volume corresponding to immersion of the electrodes (0.7-1.2 ml), and with KOH concentrations of up to 7 g/l, although 5-6 g/l is preferred. Decrease of 280 mu S/mu mol CO:, was obtained at 27 degrees C for a KOH concentration ranging from 0.5 to 8 g/l. All these results were slightly affected by temperature. However, it would be preferable for the CO2 produced to be bubbled directly into the KOH solution, in order to decrease the dynamic response of the system (gaseous transfer).