Two homofermentative strains, Lactobacillus casei NRRL B-441 and Lactobacillus casei subsp. rhamnosus NRRL B-445 were selected for further study from 17 lactic acid bacterial strains screened for lactic acid production. The effect of temperature on lactic acid production with the selected strains was investigated by adapting both strains to four different temperatures. The production of L(+)-lactic acid by both strains was most efficient at 37 degrees C, although with L. casei the highest lactic acid concentration was obtained at 41 degrees C. The maximal volumetric productivity with L. casei was 4.1 g l(-1) h(-1) and with L. casei subsp. rhamnosus 3.5 g l(-1) h(-1). The composition of the medium was studied in order to replace the costly yeast extract with less expensive sources of nitrogen and amino acids. From 11 different nitrogen sources investigated at 37 degrees C, barley malt sprouts (88 g l(-1) lactic acid in 66 h) and grass extract (74 g l(-1) lactic acid in 73 h) were the best economic alternatives. The effect of different combinations of yeast extract, peptone and malt sprouts was further studied by using statistical experimental design, and an empirical second-order polynomial model was constructed on the basis of the results. With the right combination most of the yeast extract could be substituted by barley malt sprouts for efficient lactic acid production. A method for extraction of nutrients and growth factors from malt sprouts is also described.