Recently a biocatalytic approach to enantiopure β-hydroxy-α-amino acids has been developed by application of threonine aldolases and investigated in detail in our group. In a search of potential catalysts for the asym. synthesis of α,α-dialkyl-α-amino acids, we found two natural threonine aldolases that catalyze the cleavage of racemic α-methylthreonine (1) to produce acetaldehyde and D-alanine: an L-allo-threonine aldolase from Aeromonas jandaei (L-TA) and a D-threonine aldolase from Pseudomonas sp. (D-TA). The reactions proceeded with excellent enantioselectivity: only L-1 was stereoselectively cleaved by L-TA and only the D isomers were accepted by D-TA. Having identified potential donors, we synthesized β-hydroxy-α,α-dialkyl-α-amino acids starting from a range of aldehydes as acceptors and D-alanine, D-serine, or D-cysteine as donors. A wide range of L- and D-α-alkylserine derivs. were successfully produced with excellent enantiospecificity at the α-carbon atom. Our results represent the first example of a biocatalytic asym. aldol synthesis of α-substituted serine derivs. using threonine aldolases. Moreover, our finding offers the possibility of accessing both enantiomers by choosing either L-TA or D-TA.