(R)-2-Phenylpropanoic acid was synthesized from the racemic acid through an isomerization reaction involving resting cells of Nocardia diaphanozonaria JCM3208. The isomerization activity of the cells was enhanced 25-fold by adding 5.5 mM racemic 2-phenylpropanoic acid to the culture medium. When 5 mM racemic 2-phenylpropanoic acid was included in the reaction mixture (4 ml) containing resting cells (100 mg dry cell wt) in 25 mM K2HPO4/KH2PO4 buffer (pH 7.0) at 30degreesC for 8 h, 4.56 mM (R)-2-phenylpropanoic acid (95.8% e.e.) was formed with a 91% molar conversion yield.