The ability of acetaldehyde (90 mg l(-1)) to stimulate ethanol-stressed S. cerevisiae fermentations is examined and reasons for the effect explored. Alternative metabolic electron acceptors generated similar stimulatory effects to acetaldehyde, decreasing the ethanol-induced growth lag phase from 9 h to 3 h, suggesting a redox-driven effect. The exposure to ethanol caused an instant 60% decline in intracellular NAD(+) which was largely prevented by the addition of acetaldehyde. Furthermore, the exposure to ethanol affected glycolysis by decreasing the rate of glucose utilisation from 0.33 g glucose g(-1) biomass h(-1) to 0.11 g glucose g(-1) biomass h(-1), while the addition of acetaldehyde to an ethanol stressed culture increased this rate to 0.14 g glucose g(-1) biomass h(-1).