The D,L-lactic acid racemic mixture (1),L-LA) was used as model mixture to study the separation of the enantionters using the chiral selector N-3,5-dinitrobenzoyl-L-alanine-octylester (L-SO). Two types of membrane separation were applied, namely supported liquid membrane and chiral solid membrane. In the first case the chiral selector dissolved in toluene was physically immobilised into the polypropylene hollow fiber membrane pores. In the case of the chiral solid membrane, the selector was introduced in a ceramic disc by means of its organic solution by ultrafiltration and than toluene solvent was evaporated from the pores. After its evaporation from the membrane, the L-SO selector should remain behind on the membrane internal phase by adsorptive bound or crystalline form. Both types of membrane processes could separate the enantiomers of lactic acid. The chiral solid membrane has better separation efficiency where fluxes of the D-lactic acid were changed between 4 x 10(-4) and 15 x 10(-4) mol/(m(2) h) while the average selectivity could reach about 15. For supported liquid membrane these values were changed between 3 x 10(-6) and 4 x 10(-6) mol/(m(2) h) as well as 1.2 and 2, respectively. (C) 2004 Elsevier B.V. All rights reserved.