Aims: The physiological consequences of low external oxidoreduction potential in Leuconostoc mesenteroides were investigated. Methods and Results: Leuconostoc mesenteroides was grown under two initial oxidoreduction potential conditions (E-h7: +200 mV and -400 mV) using nitrogen and hydrogen as reducing agents. Growth was affected by E-h7 ; the lag phase increased from 1 h at an initial E-h7 of +200 mV to 6 h at an initial E-h7 of -400 mV; the maximum specific growth rate at -400 mV was 68% of the one observed at +200 mV. The NADH/NAD(+) ratio and (NADH+NAD(+) ) pool were independent of the external E-h7 . Conclusions: This study shows that changing the external oxidoreduction potential from +200 to -400 mV has a strong effect on the Leuc. mesenteroides physiology. The constancy of the maximum carbon and energetic fluxes (q(glu), q(ATP) ) under the two E-h7 conditions accompanied by the decrease of Y-X/S and Y-ATP suggested the existence of an uncoupling phenomenon, namely that some catabolized glucose and hence ATP was not associated with biomass production. Significance and Impact of the Study: This paper demonstrates the usefulness of taking into account, the effect of the oxidoreduction potential on the growth of Leuc. mesenteroides in the fermentation process.