Two brewer's yeasts and one baker's yeast grew with greater than or equal to95% (w/w) pure maltotriose as carbon source in the presence of antimycin A to block respiration. Biomass yields (0.15 and 0.24 g dry yeast g(-1) sugar, respectively, with and without antimycin A) were similar for growth on maltose and maltotriose, and yields of ethanol were 80% of stoichiometric. Yeasts harvested during growth on glucose and containing low maltose transport activity did not begin to use maltotriose in the presence of antimycin A until after a long lag phase (up to 50 h), but yeast harvested during growth on maltose, and containing high maltose transport activity, began to use maltotriose after about 25 h. Much shorter lags were observed before growth started in the absence of antimycin A.