A whole wheat flour containing bran and gluten was hydrolyzed by a commercial mixed-amylase preparation and fermented to lactic acid by two Lactococcus lactis strains and two Lactobacillus delbrueckii strains. All fermentations were kept at a constant pH of 6.0 except for one case in which the initial pH was 5.85 and then was not controlled further, thereby resulting in only 3.3 g l(-1) of lactate produced. The yield of lactate based on total sugar was 80-90% for three of the strains whereas the yield for L. delbrueckii ssp. bulgaricus was much lower. The productivities and yields increased with the addition of yeast extract for all strains, but the effect varied. Lactococcus lactis ssp. lactis ATCC 19435 showed almost the same productivity (3.0 and 3.3 g l(-1) h(-1)) without and with yeast extract, respectively. All four organisms produced mainly L-lactate. The Lactococci produced 100% L-lactate in the presence of yeast extract and Lactococcus lactis ssp. lactis ATCC 19435 produced exclusively L-lactate also in the absence of yeast extract.