The effect of overexpression of the trehalose-6-phosphate (T6P) synthase gene (TPS1) on ethanol fermentation of Saccharomyces cerevisiae has been studied at 30 and 38A degrees C. The activity of T6P synthase and the accumulation of trehalose during ethanol fermentation were significantly improved by overexpression of TPS1, and especially at 38A degrees C. Ethanol produced by transformants with and without TPS1 gene overexpression at 38A degrees C was approx. 60 and 37 g/l, respectively. The fermentation efficiency of transformants with TPS1 gene overexpression at 38A degrees C was similar to that at 30A degrees C. The critical growth temperature was increased from 36 to 42A degrees C by TPS1 gene overexpression. These results indicated that overexpression of the TPS1 gene had a beneficial effect on the fermentation capacity of the title yeast strain at high temperatures.