β-Chlorolactic acid was condensed with toluene-α-thiol to give 2-hydroxy-3-benzylthiopropanoic acid. The optical isomers were prepared by resolution with brucine and quinine. Removal of benzyl groups yielded (+)- and (–)-2-hydroxy-3-mercaptopropanoic acid. Desulphurization with Raney nickel gave (+)- and (–)-lactic acid. Configuration and optical purity of all isomers have been determined.