A fed-batch fermentation of Lactobacillus lactis to produce L-lactic acid was developed in which the residual glucose concentration in the culture was used to control a continuous feeding strategy. Up to 210 g L-lactic acid l(-1) (97% yield) was obtained. The maximal dry cell was 2.7 g l(-1) and the average L-lactic acid productivity was 2.2 g l(-1) h(-1).