The effect of ethanol on yeast growth and fermentation has been studied in two strains, NCYC479 (a commercial saké yeast) and 5D-cyc (a laboratory haploid strain). The effect of ethanol on growth was similar in the two strains. It showed complex kinetics which resulted from both the inhibition of the growth rate itself and also a reduction in cell viability. The growth and viability effects had different inhibition constants. Ethanol was less inhibitory toward fermentation than toward growth. Fermentation in the saké yeast was more ethanol tolerant than in the laboratory strain. The inhibition kinetics for fermentation were less complex than those for growth and followed the classical noncompetitive pattern.