.beta.-Hydroxy-.alpha.-amino acids are obtained via serine hydroxymethyltransferase catalyzed condensation of aldehydes with glycine. The predominant product with most aldehydes is the L-erythro diastereomer. For example, succinic semialdehyde methylester is condensed with glycine in the process to provide L-erythro .alpha.-amino hydroxy adipic acid mono methyl ester.