BACKGROUND: Microbial cells have been used widely in biosynthesis of chiral alcohols. However, research concerning the effect of oxygen supply in cultivation on biocatalytic activity of whole cells in organic synthesis is limited. This study improved the reaction efficiency of Candida parapsilosis catalyzing (R,S)-1-phenyl-1,2-ethanediol (PED) deracemization by controlling agitation during cell cultivation. RESULTS: The increase of dissolved oxygen concentration by adjusting agitation speed from 200 to 300 rpm at aeration rate 1.5 vvm significantly improved the cell growth of C. parapsilosis and the activities of two key enzymes involved in deracemization. (S)-PED with higher optical purity of 98.23%e.e. and yield of 82.94% was formed. Compared with the initial fermentation conditions at aeration rate 0.75 vvm and agitation speed 200 rpm, enhanced oxygen supply conditions afforded better cells for highly efficient conversion under higher substrate concentration. CONCLUSION: Oxygen supply had a significant effect on cell growth and catalytic activity of C.parapsilosis catalyzing asymmetric oxidoreduction. By conveniently controlling agitation in cultivation, cell activity and key enzymes production for a complex reaction of concurrent tandem oxidation and reduction processes can easily be conducted, which could help to cultivate cells catalyzing synthesis of interested chiral compounds. (C) 2008 Society of Chemical Industry