The microbial degradation of L-methionine was investigated in order to develop a practical process for D-methionine production from racemic methionines. Among thp 1000 culture strains tested, microorganisms belonging to the Achromobacter, Bacillus, Micrococcus, Morganella, Proteus, Providencia, Pseudomonas and Sarcina genera exhibited a high L-methionine-degrading activity. Proteus vulgaris IAM 12003 was determined to be the best strain and was used as a biocatalyst for eliminating the L-isomer. The degradation of L-isomer in this P. vulgaris IAM 12003 cell was assured by the action of L-amino acid oxidase. The maximum rate of L-isomer degradation was obtained at 30 degrees C and pH 8.0. Under these optimal conditions, the L-isomer in a 100 g/l mixture of racemic methionines was almost degraded within 20 h, with 46.5 g D-methionine/l remaining in the reaction mixture. Crystalline D-methionine, with a chemical purity greater than 99% and optical purity of 99.9% enantiomeric excess, was obtained at a yield of 30% from the reaction mixture by simple purification.