Casein whey permeate (CWP), a lactose-enriched dairy waste effluent, is a viable feed stock for the production of value-added products. Two lactic acid bacteria were cultivated in a synthetic casein whey permeate medium with or without pH control. Lactobacillus lactis ATCC 4797 produced d-lactic acid (DLA) at 12.5 g l(-1) in a bioreactor. The values of Leudking-Piret model parameters suggested that lactate was a growth-associated product. Batch fermentation was also performed employing CWP (35 g lactose l(-1)) with casein hydrolysate as a nitrogen supplement in a bioreactor. After 40 h, L. lactis produced 24.3 g lactic acid l(-1) with an optical purity > 98 %. Thus CWP may be regarded as a potential feed-stock for DLA production.