Extracellular reduction of menadione and ferricyanide were promoted by glucose rather than ethanol in a yeast cell (Saccharomyces cerevisiae IFO 2044) suspension. NAD(P)H : menadione oxidoreductase from yeast plasma membrane possessing ferricyanide reductase activity had higher substrate specificity for NADH than for NADPH. Glucose produced a transient increase in NADH content in the absence of menadione, but neither glucose nor ethanol restored the NADH content upon menadione-catalyzed ferricyanide reduction. These findings suggest that the NADH content is controlled by the metabolism of glucose and ethanol, and that the excess of NADH generated by glucose and ethanol is effectively consumed by NADH:menadione oxidoreductase in the yeast transplasma membrane redox system.