Process variables were optimized for the production of lactic acid from pretreated beet molasses by Lacrobacillus delbrueckii IFO 3202 for batch and continuous fermentations. In the batch fermentation, maximum yields (95. 4% conversion, 77.1% effective) and maximum lactic acid volumetric productivity (483 g dm(-3) h(-1)) was achieved at 45 degrees C, pH 6.0, 78.2 g dm(-3) sugar concentration with 10 g dm(-3) yeast extract. Various cheaper nitrogen sources were replaced with yeast extract on equal nitrogen bases in batch fermentation. Of all the nitrogen sources tested, yeast extract yielded the highest and malt sprouts yielded the second highest level of lactic acid. In the continuous fermentation, maximum lactic acid (4.15%) was obtained at a dilution rate of 0.1 h(-1). Maximum volumetric lactic acid productivity (11.20 g dm(-3) h(-1)) occurred at D = 0.5 h(-1) dilution rate.