We have developed an enzymatic procedure for the enantiospecific synthesis of N-acetyl-L-methionine with aminoacylase in an organic solvent. N-Acetyl-L-methionine was most effectively synthesized with a yield of about 90% (on the basis of the L-methionine used) when the reaction mixture, composed of 100 mM sodium acetate, 20 mM DL-methionine and aminoacylase (1000 units) immobilized on celite in 1 ml ethyl acetate saturated with 32 mu 1 40 mM sodium phosphate buffer (pH 7.0) containing 0.1 mM CoCl2, was incubated at 30 degrees C for 24 h. N-Acetyl-L-methionine was isolated from the reaction mixture and the enantiomeric excess was 100%. D-Methionine was also isolated from the mixture with a yield of about 95% and 90% enantiomeric excess. The method is applicable to the synthesis of other N-acetyl-L-amino acids.