Lactobacillus delbrueckii was grown at room temperature in static culture. When whey (total sugar 30 g l(-1)) was supplemented with different concentrations of yeast extract, lactic acid production increased. When glucose (20 g l(-1)) was added to whey; 20 g l(-1) yeast extract supplementation was found to be most suitable. Among the different nitrogen sources supplemented to whey [yeast extract, peptone, soya flour, and (NH4)(2)SO4, having the same elemental nitrogen level of 3.1 g l(-1)], yeast extract was the best. The effect of yeast extract could be due to its vitamin B content. Therefore, whey was supplemented with different nitrogen sources and vitamin B complex, and no significant improvement in lactic acid production was observed. As yeast extract supplementation was not economically attractive, we decided to use a proportion of (NH4)(2)SO4 and yeast extract. When the elemental nitrogen ratio of (NH4)(2)SO4 to yeast extract was 3:1, the substrate use and efficiency of lactic acid production were same as in whey supplemented with 20 g l(-1) yeast extract.